WASHINGTON — It's election season, and Hillary Clinton and John McCain are political foes once again. Once Clinton's favorite Republican, McCain has ripped the Democratic presidential nominee as a liar about Benghazi and vowed to block her Supreme Court nominees, while Clinton and her surrogates have rallied with the Arizona Republican senator's Democratic rival and used McCain as a cudgel against Donald Trump.

Clinton on Wednesday held a rally at Arizona State University, where she declared the traditionally red state winnable for Democrats.

The two battle-tested political titans have eight years of history as colleagues in the Senate, where they were traveling companions, even drinking buddies (sort of) — with many warm words between them. With both leading in the polls, and McCain's Senate Armed Services Committee chairmanship tied to the prospect that Republicans could lose their Senate majority, his supporters say that post-Nov. 8, he should revive their rapport to become a broker between the White House and a Congress likely to continue to be bitterly divided.

"He needs to be the guy to step up and be a statesman to work with the president on the issues they agree upon. I hope he will, but we'll see," former Arizona Attorney General Grant Woods, a longtime friend of McCain's and his first congressional chief of staff, told Defense News.

Woods, who crossed the aisle to endorse Clinton, pressed McCain in a recent conversation to be "the linchpin and the bridge" for bipartisan progress in Congress, "to move the country forward." If this is to be 80-year-old McCain's last term, it is more likely he will want to spend it cementing his legacy than in partisan obstruction, Woods said. 

"At this point of his life, he will be interested first and foremost in getting things accomplished," Woods said. "He could be a key ally for the president, but if they're not [friends], we could have more of the same."

McCain, who is notoriously prickly, must be handled with care. While the Obama administration had fumbled a potential alliance, Woods said, the right move after Nov. 8 would be for Clinton — if she and McCain prevail — to reach out personally and have their staffs work together on common interests.

"The next administration would be wise to cultivate that relationship as much as possible, to pay attention to it and give him the respect he deserves," Woods said. "If they don't do that, things can go the other way."

Clinton has vowed to reach out to Republican lawmakers. Should she become president, she will face the daunting task of dealing with a Congress in which Republicans will likely control the House and have enough votes in the Senate to obstruct her legislative priorities. In that scenario, McCain, whose reelection was in doubt just months ago, could stay a major power player whether or not he is Senate Armed Services Committee chairman.

Former Marine Corps major general and SASC staff director Arnold Punaro, who supports both Clinton and McCain, believes the duo has the potential to broker a grand bipartisan bargain. That is, the long-sought-after deal over entitlement spending and revenues—if not other shared-but-politically-charged priorities like immigration reform and a strategy for Syria. 

"There are a lot of things he might oppose her on, but I could see him doing something very bold [together with Clinton]," Punaro said. 

Clinton and McCain both favor an end to statutory budget caps, which Clinton has  ripped as "arbitrary." While Clinton is  less hawkish on nuclear modernization  than McCain, both campaigns' web sites promise to maintain the best trained and equipped military in the world. (Pentagon brass respect Clinton as "an ardent advocate of a strong military" who "believed in all forms of American power, including force," according to the biography "HRC.")

A former senior aide to Clinton felt the two might work together on across a broad array of policy areas, anything related to the military, veterans, national security or immigration. 

"I genuinely think it's from A to Z, name your issue, name your vehicle that requires negotiation to cross the finish line," the former aide said. "They're both really smart and in the job to get things done. They have knowledge, a regard and even an affection for one another. Those are the ingredients for what now is a four letter word: compromise and negotiation."

A public embrace before the election is all but impossible. Clinton has redirected more than $2 million in campaign cash to turn long-red Arizona blue, and she and her surrogates have campaigned with McCain’s challenger for reelection, Rep. Ann Kirkpatrick. Not only would boosting Democratic turnout threaten McCain, but Clinton’s daughter Chelsea, at a Democratic rally Oct. 19 at Arizona State University, touteda win for Kirkpatrick and a Democratic Senate as instrumental to her mom’s agenda.

Clinton, in her first visit of the general election to the Grand Canyon State, did not mention McCain by name but told the audience at her Arizona State University rally that Kirkpatrick would be the independent voice Arizona deserved, and said that Kirkpatrick, "unlike her opponent, has never been afraid to stand up to Donald Trump."

Recent polling puts Clinton and Trump in a virtual tie for Arizona's electoral votes, and after FBI Director James Comey sent a letter to certain members of Congress about a new development in the long-running Hillary Clinton email mess, the University Center for Politics changed the state's general election rating from "leans Democrat" to "toss-up."

Clinton's chances in Arizona largely hinge on the state’s rapidly growing Hispanic population, a group Trump has offended throughout the campaign with anti-immigration rhetoric. More than 20 percent of eligible voters in Arizona are Hispanic, according to Pew Hispanic, but turnout rates promise tolag behind those of other groups.

Clinton spokesman Brian Fallon tweeted last week, "Arizona ain't an indulgence. It's a true battleground. Perhaps even more favorable-looking right now than some other places we've been on TV."

In the Senate race, McCain leads Kirkpatrick at 48-40 percent, according to a Real Clear Politics polling average, though his numbers could suffer if Democratic turnout surges.

Though McCain has dropped even his tepid support for Donald Trump, he has explicitly campaigned as "a check, not a rubber stamp" on a Clinton presidency, evidenced by a glossy, five-minute video released a day after he won the state's GOP primary in late August. 

In his first serious reelection fight, with a candidate buoyed by anti-Trump sentiment, McCain has had to artfully dance through this year's unusual cross-cutting political currents. Despite Trump's insults to McCain's Vietnam POW status, McCain endorsed him as the GOP's nominee to avoid alienating GOP voters, alternately dodging questions on Trump and criticizing him before rebuking Trump entirely for his vulgar comments in a 2005 video that surfaced in early October.

The bond and mutual respect between Clinton and McCain was forged during the time together on the Senate Armed Services Committee. On a personal level, the two connected over an admiration for the military and while on official travel. On a practical level, they shared an pragmatic acknowledgment that being effective in Congress takes bipartisanship.

"I think the best of each of them came out when they spent time together," Clinton's former aide said, adding: "She and he were all about getting things done and not wasting time. Those personal connections in Congress come when people are workhorses, not show horses."

When Clinton and McCain met in the early aughts, he was at peak maverick, frequently crossing party lines, a master of political triangulation and perhaps the Senate's most influential member, the New York Times later said. Clinton, then the junior senator from New York known primarily as the first lady at first, took a seat on the SASC in 2003 with the 9/11 terrorist attacks heavily on her mind and went on establish her current reputation as a hawkish centrist.

The two lawmakers with obvious star power attracted media attention for their shared trips to Iraq, Afghanistan, the Yukon, and the Baltics—where they allegedly traded shots of vodka in an Estonian restaurant in 2006.

That tale surfaced in the New York Times as the 2008 election season took off and again ahead of the 2016 election, in a humanizing video posted to the Clinton campaign's Facebook page.

"We have our political differences, but we sat there drinking vodka until we both agreed to withdraw in honorable fashion, I think after having reached the limits that either of us should have," Clinton chuckled. 

In 2005, Clinton and McCain appeared via satellite from Iraq on "Meet the Press," where Tim Russert asked them whether the other would make a good president. They played along, evincing a rapport that led Russert to joke the two should form a fusion ticket.

WASHINGTON - MARCH 27: Sen. John McCain (R-AZ) (3rd L) smiles as Sen. Hillary Clinton (D-NY) (2nd R) reacts to him getting on the same elevator after a vote at the US Capitol March 27, 2007 in Washington, DC. Both senators have announced they are running for the US presidency. The Democrats successfully voted down 48-50 an amendment by Sen. Thad Cochran (R-MS) to remove an troop withdrawal date from an Iraq spending bill. (Photo by Chip Somodevilla/Getty Images)
WASHINGTON - MARCH 27: Sen. John McCain (R-AZ) (3rd L) smiles as Sen. Hillary Clinton (D-NY) (2nd R) reacts to him getting on the same elevator after a vote at the US Capitol March 27, 2007 in Washington, DC. Both senators have announced they are running for the US presidency. The Democrats successfully voted down 48-50 an amendment by Sen. Thad Cochran (R-MS) to remove an troop withdrawal date from an Iraq spending bill. (Photo by Chip Somodevilla/Getty Images)

Sen. John McCain, R-Ariz., (3rd L) smiles as then-Sen. Hillary Clinton, D-N.Y. (2nd R), reacts to him getting on the same elevator after a vote at the US Capitol March 27, 2007 in Washington, D.C. Both senators have announced they are running for the US presidency.

Photo Credit: Chip Somodevilla/Getty Images

When the two actually were presidential candidates in 2008, McCain largely held fire against Clinton as she brawled with Obama for the Democratic nomination. McCain did make a solo appearance on "Meet the Press" in which he  knocked Clinton's plan for withdrawing US troops from Iraq as "surrender," and Clinton had a "no McCain" applause line in her Democratic National Convention speech that year. 

After the 2008 election, in which Obama bested Clinton for the Democratic nomination and McCain in the general election, Obama tapped Clinton to be his secretary of state—but she was not immediately confirmed. When McCain's Republican colleagues sought to block Clinton's nomination, McCain made a Senate floor speech on Jan. 21, 2009, urging them to immediately confirm the "obviously qualified" Clinton. "The message the American people are sending us now is they want us to work together and get to work," he said.

As secretary of state, Clinton may have been the administration's most reliable advocate for military action, Time observed. "Clinton backed a bold escalation of the Afghanistan war. She pressed Obama to arm the Syrian rebels, and later endorsed air strikes against the Assad regime. She backed intervention in Libya, and her State Department helped enable Obama's expansion of lethal drone strikes. ... On at least three crucial issues—Afghanistan, Libya, and the bin Laden raid—Clinton took a more aggressive line than [Defense Secretary Robert] Gates, a Bush-appointed Republican."

Clinton had a reputation as secretary of state for getting along with lawmakers of both stripes, in both houses. At a 2011 Christian Science Monitor breakfast, McCain  said Clinton was an "international star" who "has done a really tremendous job." He saved the criticism for President Obama, on the administration's Libya plan.

In 2012, Politico reported Clinton's friendship with McCain helped shield her from GOP fire amid the politically-fueled Benghazi fracas. The supposed offense was incorrectly characterizing the attack on the US Consulate in Libya as sparked by spontaneous protests rather than a deliberate act of terrorism. At the time, McCain was one of the most vocal critics of the administration on Benghazi, but he preferred to blame the White House over Clinton.

As Clinton was leaving office as secretary of state, McCain looked back on their time in the Senate, telling Politico, "She and I seemed to hit it off with each other and enjoy each other's company," and that "of course" she is qualified to be president. Lauding her as a policy wonk akin to her husband, McCain said, "She puts people at ease, she is a role model to a lot of young women in America — my daughter [Meghan] admires her a great deal."

In June 2014, Clinton appeared on "Good Morning America" to promote the memoir "Hard Choices," when host Robin Roberts asked to name her favorite Republican. It was McCain.

"Despite my problems sometimes with him, John McCain, because we have traveled a lot, and we argue a lot, and he goes off on something that I disagree with, but I admire him and I've spent a lot of time with him," she said.

In the memoir itself, Clinton had praised McCain for a Senate floor speech in which he denounced Rep. Michele Bachmann and four other House Republicans for alleging longtime Clinton aide Huma Abedin was a member of the Muslim Brotherhood. She also praised Obama for his defense of Abedin.

"The President of the United States and one of our nation's most renowned war heroes make quite a one-two punch," she wrote.

"Face the Nation" host Bob Schieffer asked McCain weeks later whether Clinton was his favorite Democrat, and McCain chuckled, joking he hoped his comments would be cut in his red-leaning state.

"I respect Secretary/Senator Clinton; I respect her views," McCain said. "We have had disagreements on a number of issues. But I think it's my job to work with every president if she, regrettably, attains the presidency. I worked with her in the Senate, I just worked with [Vermont Democrat] Sen. [Bernie] Sanders on a Veterans Affairs bill.

McCain had been a member of the "Gang of Eight" senators seeking a bipartisan compromise on immigration reform and he bucked the GOP strategy that led to the government shutdown of 2013—both of which earned him a censure from the Arizona Republican Party.

"You've got to reach across the aisle and work together on certain issues," McCain told Schieffer. "And I'm not only not embarrassed about that. I'm proud of it. And I respect Hillary Clinton. I may not agree with her."

But McCain's last big U-Turn on Clinton came as he announced his reelection bid in 2015, just after Clinton announced her second presidential run. After praising Clinton's time as secretary of state, he was now calling her tenure at the State Department a big nothing.

"I think that a legitimate question to Hillary Clinton is, 'What did you accomplish during your four years as secretary of state? Except that you visited more countries than any other previous secretary of state. What was your accomplishment?'" he said. "So far, I don't know what an answer to that would be."

Though McCain was scraping the old friendship off his shoe, it still served Clinton to tout it as a touchstone of her bipartisan bonafides. After announcing her 2016 run, she told the Concord Monitor she worked well with McCain and the hawkishly moderate Sen. Lindsey Graham, R-S.C.

"Now, we'll go through the political season, and they'll be cringing when I say I worked well with them. But my co-sponsor on healthcare for the National Guard and Reserve was Lindsey Graham," Clinton said. "And he may not want to be reminded of it, but we worked really hard to get that done."

U.S. Secretary of State Hillary Clinton testifies before the Senate Foreign Relations Committee about the September 11 attacks against the U.S. mission in Benghazi, Libya, on Capitol Hill January 23, 2013 in Washington, DC. Lawmakers questioned Clinton about the security failures that led to the death of four Americans, including U.S. Ambassador Christopher Stevens.

Photo Credit: Getty Images

Clinton was right about campaign season. In recent months, McCain has saidneither Clinton nor Trump had the right military strategy to beat Islamic terrorism, and later that Republicans would automatically oppose any of her Supreme Court nominees. (His camp quickly walked that back.) He even undercutClinton’s claims of advocacy for veterans.

"To my knowledge, I know of no activity, legislative or otherwise, that Hillary Clinton was engaged in during her time as United States senator," he said. "I don't see how any veteran who cares about their fellow veterans could possibly have any good things, nor could support, her quest for being commander-in-chief."

Stinging stuff after Clinton, during September's Commander-In-Chief Forum, touted her work with McCain to raise money for a Brooke Army Medical Center unit for amputees and burn victims who served in Iraq and Afghanistan. The two were photographed together at the opening in 2008.

McCain's toughest talk came in his only televised debate with Kirkpatrick, when he repeated claims Clinton had lied about the nature of the Benghazi attack to the victims' families, while standing over their coffins. 

"Hillary Clinton has told lies after lies. Hillary Clinton has disqualified herself to be president of the United States," McCain said, equating her conduct to Trump's worst. "Lying to the grieving family: That to me is not unlike Mr. Trump demeaning and degrading women, as well as Muslims, disabled people, prisoners of war."

In an email to her daughter Chelsea on the night of the attack, Clinton had blamed al-Qaeda, but in discussions with families, she said the cause was protests. She has since said information officials were receiving that night was contradictory, "changing, literally, by the hour."

In July, when McCain appeared on KTAR's "The Think Tank," the hosts reminded him he had praised Clinton in a past interview as a "rock star who did a fine job as secretary of state." Benghazi, he told them by way of explanation, had changed his mind. He had been friends with the slain US Ambassador to Libya, Chris Stevens, and Clinton had lied to his family, he said.

"That negates a lot of her work as secretary of state, and I believe all this information about the use of her server is damning, because she obviously did not tell the truth," McCain said, insisting, "You can't take that off the table."

Mike O'Neil, a Think Tank co-host and Arizona-based political analyst, told Defense News he didn't buy it. The friendship and ideological alignment are too strong for McCain to have had a sincere change of heart. Instead, McCain must have been tacking right to appease his conservative base and survive an upcoming primary challenge.

"Yes, you heard what he said on my show, but I think he was looking for an opportunity to diss her for partisan consumption," O'Neil said. "If you have a long, enduring, multi-year relationship with somebody — you travel together, you see the world the same — and then something like Benghazi happens, you say, 'There was a screw-up there, but her involvement was peripheral-to-none when you strip away the partisanship.'"

Over his 25 years in the Senate, McCain has had enough politically canny transformations that he is hard to know, O'Neil said. Those same political instincts, however, may yet lead McCain to reconcile with Clinton. She will need someone like him to help push through legislation, and in exchange, she could help secure McCain's ambitious defense reform agenda—and abet his becoming the maverick once again.

"If you're a Democrat, having a friend or two on the other side certainly could be a cushion," O'Neil said. "If he decides not to run again, he can be as much of a free agent as he cares to be."

Email:  jgould@defensenews.com

Twitter:  @reporterjoe