WASHINGTON — President Trump's first 2018 budget blueprint was panned on both sides of the aisle on Tuesday, but a key Senate Democrat said his party could support Trump's defense proposal if the domestic side is raised to match.

If a $603 billion top line for the base defense budget and a $462 billion top line for the domestic side of the budget is Trump's opening position, the opening position for Senate Democrats is familiar one: Parity between the defense and non-defense budgets. 

Sen. Richard Durbin, the Senate's No. 2 Democrat and the chairman of the Senate Appropriations Defense Subcommittee, told reporters Tuesday if that were the case, Democrats "would have a more open mind." 

Restoring military readiness — which has "suffered through sequestration and the other budget cuts" — is the number one priority, with weapons systems and modernization up for conversation, Durbin said.

"But unless there is some sort of parallel investment on the non-defense side, many of us are going to resist it," said Durbin, of Illinois. 

On the flip side, an increase for the non-defense side is likely to run afoul of fiscally conservative Republicans.

The Trump White House was dealt a a blow Tuesday as senior Senate Republicans joined Democrats to push back on the budget blueprint.

Senate Majority Leader Mitch McConnell, R-Ky., told reporters that deep State Department cuts Trump is expected to propose "probably" can't pass the upper chamber.

"When we get to funding the government, obviously it will be done on a bipartisan basis," McConnell said, adding he believes the "diplomatic portion of the federal budget is very important."

The Wall Street Journal reported the Trump administration will cut the State Department and the U.S. Agency for International Development by 37 percent.

Sen. Lindsey Graham, who is the chairman of the Senate Foreign Relations subcommittee that oversees foreign aid, told NBC News the proposal was "dead on arrival."

"It's not going to happen," said Graham , R-S.C. "It would be a disaster."

On Monday, more than  120 retired three and four-star generals organized by the U.S. Global Leadership Coalition sent a letter to the House and Senate leadership to urge them to protect the State Department and USAID budgets.

The House Armed Services Committee Chairman Rep. Mac Thornberry, R-Texas, and his Senate counterpart Sen. John McCain, R-Ariz., have criticized the Trump blueprint as insufficient on defense spending.

The two hawkish lawmakers have proposed $640 billion for the 2018 base defense budget, and McCain has noted that Trump top-line is a "mere" 3 percent over President Obama's 2017 request for $583 billion.

Echoing comments from key Democrats and Republicans, defense budget analyst Todd Harrison, of the Center for Strategic and International Studies, called the budget blueprint a "starting point" for the Trump administration's negotiations. Harrison's read was it means less for defense in a final deal.

"In all likelihood we're not going to get as much money for defense as the Trump administration is proposing right now," Harrison said.

To spend more on defense than the budget caps allow requires 60 votes in the Senate, which requires a deal with Democrats. Harrison noted that every deal for the last five years has modified budget caps with parity between defense and non-defense as a prerequisite for a deal.

One key development is Senate Democrats are "close to an agreement" for leftover 2017 appropriations for the Defense Department that would exceed President Obama's budget request, Durbin said, to "come up with bipartisan answers, that are reasonable."

Other lawmakers confirmed the bill will match the 2017 defense policy bill that passed Congress in December at $618.7 billion.

A Senate Appropriations Committee spokesman affirmed that Chairman Sen. Thad Cochran, R-Miss., "is pleased with progress between the House and Senate to complete the 2017 defense bill, and would like to see similar progress on the remaining bills."

Congress punted on most 2017 spending bills last year in favor of a stopgap spending bill that expires at the end of April. Without a 2017 spending bill, Congress would either shut down the government or pass another stopgap continuing resolution.

Durbin said he did not know whether McConnell is on board with the 2017 appropriations in the works, but he was optimistic that the defense bill would be able to navigate Capitol Hill's partisan crosscurrents:

"I hope so, but it started with a lot of hard work between House and Senate Democrats and Republicans," he said. "A CR is a terrible way to run the Department of Defense or any branch of government."

Asked about the White House's soon-to-come $30 billion defense supplemental spending bill, Durbin would not say whether Democrats would insist on parity. President Trump and his surrogates have repeatedly promised the supplemental would come within the first 100 days of the administration.

"We want to know where it's coming from … if they're paying for it, and if the next budget will take it out of non-defense spending," Durbin said. "If he is going to give more money to the Department of Defense at the expense of the National Institutes of Health, medical research, we're going to have a fight on our hands."

Nor could Durbin say whether the supplemental would ultimately be wrapped into the 2017 spending bill itself or be part of 2018 appropriations.

"We don't know why it's been held up. They've been teasing us with it for weeks. It seems pretty straight forward, but maybe paying for it isn't," Durbin said.

Senior Pentagon Correspondent  Aaron Mehta contributed to this report.

Email:   jgould@defensenews.com     

Twitter:   @reporterjoe     

Joe Gould is the Congress and industry reporter at Defense News, covering defense budget and policy matters on Capitol Hill as well as industry news.

More In Congress
‘No way around it’: Facing budget cuts, Army braces to fight for modernization
As budget experts caution the Army will see reduced or — at best — flat budgets in the coming years, service officials are readying for a more difficult look at how to cut costs to preserve modernization momentum. This could mean making harder decisions about the future of its inventory or making cuts to reduce readiness or end strength.