WASHINGTON — White House budget director Mick Mulvaney is expected to release his 2018 budget blueprint on Thursday, but it is already getting pushback on Capitol Hill.

Analysts say the so-called "skinny budget" and its inclusion of $603 billion for the Pentagon — a $54 billion defense boost paid for by cutting most non-defense accounts, including foreign aid — is one of many items likely to shift before lawmakers can find their way to a bipartisan deal.

"I don't think much of what will be proposed on Thursday will get through as proposed, and a lot of suggestions are going to be dead on arrival when they hit the Congress," Jim Moran, a former Democratic congressman from Virginia who served for many years on the House Appropriations Committee, told Defense News.

That's in part because breaking the firewall between defense and non-defense, as spelled out in the 2011 Budget Control Act, would need Democratic support to reach 60 votes in the Senate.

With that leverage, Democrats say they will fight for parity between the defense and non-defense sides and block GOP plans to fund President Trump's border wall — a recipe for a stalemate with conservative lawmakers.

How does this play out for the Pentagon budget? "I think it gets compromised down to a relatively marginal increase for defense," Moran said.

There is also pressure to boost defense, as hawkish lawmakers have criticized the $603 billion top-line for defense as only 3 percent, or $18 billion, above the Obama administration's plan.

Senate Armed Services Chairman John McCain, R-Ariz., and his House counterpart, Rep. Mac Thornberry, R-Texas, have argued a $640 billion top-line would replenish a military depleted by the Obama presidency—an unlikely prospect by Moran’s reckoning.

On Tuesday, McCain took a hard line arguing for a defense boost to repair fleet readiness and maintenance, whether or not Mulvaney is on board.

"I'm not changing," McCain told reporters. "If they want to ignore the judgement of our military leaders that says our men and women in uniform are at greater risk, that's their problem."

Plans for a $2 billion cut for the Transportation Security Administration and Coast Guard have netted criticism from both sides of the aisle. Among them, House Coast Guard and Maritime subcommittee Chairman Rep. Duncan Hunter, R-Calif., has led efforts against a $1.3 billion cut for the Coast Guard, calling it "nonsensical."

A Trump ally on the SASC, Sen. Thom Tillis, R-N.C., called the White House blueprint "the beginning of a dialogue where the end result looks very different from the president's budget and the budgets we'll move forward here in the Congress." He signaled a focus on plussing up readiness and modernization.

"I don't know that it even scratches the surface if we're going to continue the operations tempo we've had over the last decade or more," Tillis said. "The question is whether we have a candid discussion about the whole of the budget .... We have to fix mandatory spending problems too."

But would lawmakers be willing to brave the political crosscurrents that come with targeting safety net programs like Social Security, Medicare and Medicaid?

Congress might be able to skirt the toughest conversations by managing the defense increase through the use of the Overseas Contingency Operations account, which is exempt from budget caps. It's the sort of move Mulvaney has opposed before, and it would invite Democrats to insist increased defense spending be matched on the domestic side of the budget, as they have in recent budget deals.

Roger Zakheim, a visiting fellow at the conservative American Enterprise Institute (AEI), said that "for sure" OCO will end up playing a part in the budget discussions, despite Mulvaney's previous attempts to restrict the use of the funding mechanism. That is largely due to the nature of OCO as a way to get around a confrontation of the fiscal hawks and the defense hawks, he said. 

If Speaker Paul Ryan has to choose between a showdown in his own caucus or telling the defense hawks that "for now can you pick your number of billions and let me throw it into OCO, [Ryan] probably takes that deal," Zakheim predicted at an AEI event Tuesday. 

Zakheim's colleague at AEI, Mackenzie Eaglen, also predicted that F-35 joint strike fighters and F/A-18 Super Hornets will be included in this wave of OCO funding, despite the focus of that funding supposedly being near-term warfighting requirements. 

"It's ironic that as OMB director [Mulvaney] came in, wanted to prioritize disciplined OCO because he'd been so aggressive on the discretionary side and not giving this commensurate increase on non-defense and defense, [which] will result, I predict, in an OCO that is less disciplined and larger than they're going to come in with," Zakheim said. 

How does a thinner defense budget square with Trump's campaign promise to rebuild the military? It's unlikely Thursday's blueprint will provide details about future defense budgets—which are expected in Trump's larger budget submission in May.

Mark Cancian, of the Center for Strategic and International Studies, estimates it will cost about $80 billion to get the force Trump has described — with a regular Army of 540,000 soldiers, a Navy of 350 ships, a Marine Corps of 36 active-duty infantry battalions, and an Air Force of 1,200 active tactical fighter/attack aircraft, plus enhanced missile defense and cyber capabilities

If the increase turns out to be $18 billion per year, "you could barely afford the current force and won't have much of a buildup at all," Cancian told Defense News.

At the AEI event, Eaglen put it bluntly, saying the first Trump budget is going to "please no one."

"It's not going to please fiscal hawks because it's really a status quo, it's not going to please defense hawks because they are going to see it as a flat line year over year," she said. "It's at best an inflation adjusted defense budget. It could possibly be negative real growth, which I think would shock the president, who wants to do different things with that money. I've got news for him: He's not going to be able to do that."    

The State Department is reportedly facing steep cuts, which has sparked concerns from lawmakers and national security veterans about America's ability to promote its values around the world and avert wars, rather than fight them. Sen. Marco Rubio, R-Fla., took to the Senate floor to describe foreign aid as a national security imperative.

"I promise you, it's going to be a lot harder to recruit someone to anti-Americanism and anti-American terrorism if the United States of America was the reason why they are even alive today," said Rubio, a Senate Foreign Relations Committee member.

Senators have also warned that plans to kill U.S. subsidies for foreign allies to buy American-made weapons outright and replace them with a loans program would kill defense industry jobs. The idea would not apply to the security aid committed to Israel — which makes up more than half of the $5.7 billion program.

As a practical matter, Moran predicted powerful appropriators will balk at cuts in their spheres of control—like Rep. Hal Rogers, R-Ky., the former House Appropriations Committee chairman and now chairman of its Subcommittee on State and Foreign Operations Subcommittee. The subcommittee's former chair is Rep. Kay Granger, R-Texas, who now chairs the Defense Subcommittee.

Sen. Lindsey Graham, chairman of the Senate Appropriations Subcommittee on State and Foreign Operations, earlier this month said deep State Department cuts are "dead on arrival" in Congress.

"I don't think these are things the president fully understands—the makeup of the Congress and the internal politics of the Congress," Moran said. "I would be shocked if those cuts were allowed to take place."

— Aaron Mehta in Washington contributed to this report.