With a little more than 100 days left to avoid a government shutdown, the federal budget process is about to lurch to a halt and it remains unclear who can get it going again.

Senate Democrats are promising to filibuster all of the annual appropriations bills — including the Defense bill teed up by Majority Leader Mitch McConnell, R-Ky., until Republicans agree to spend more money on domestic programs.

The question is at what point do real negotiations start — and who does the negotiating.

Last time, Sen. Patty Murray, D-Wash., and Rep. Paul D. Ryan, R-Wis., took the lead in negotiating a relatively small-in-scope spending deal — and the two budget chairmen were the obvious choice. This time could play out differently, especially if there’s a larger deal that clears the decks through the end of Obama’s presidency.

But ambitions for a big or even medium deal may already be shrinking given the difficulty of getting offsets for the relatively tiny Trade Adjustment Assistance program.

Ryan is no longer chairman of the House Budget Committee and new Chairman Tom Price, R-Ga., seems to have the confidence of House Republican leadership. House Democrats could continue to put their faith in ranking member Chris Van Hollen, D-Md., though Minority Leader Nancy Pelosi, D-Calif., will surely play a key part, as she has been repeatedly needed to come up with the votes for previous deals up until last week’s trade snafu.

But Boehner has often put the onus on the White House to take the lead, saying on June 11 that “If [President Barack Obama] wants to have a budget negotiation, all he has to do is ask.”

In the Senate, Murray has also rotated out of her post atop the Budget Committee, clearing the way for presidential hopeful, Sen. Bernard Sanders, I-Vt. But Murray would still be a natural choice, with her budget knowledge, negotiating experience and leadership post as the No. 4 Democrat.

She sounded like a willing negotiator last week.

“The choice is in Republican leaders’ hands. Work together now and avoid a crisis — or work together later while we’re in a crisis. It’s up to Republican leaders — and all that Democrats, families, and businesses across the country can do is keep the pressure on and hope that they make the right decision,” Murray said in a June 10 speech.

The Democrat from Washington outlined what an agreement should look like, saying there wouldn’t necessarily need to be a big deal, but she did make another push for revenue — anathema to the GOP.

“Of course, I have some ideas about where that revenue should come from,” Murray said. “Surely we can find one or two of the most egregious and wasteful tax loopholes to close to pay for these important investments. But as Democrats demonstrated in 2013, if they can’t agree to close a single wasteful loophole then we are open to Republican ideas about where that revenue can come from — as long as the deal is truly fair for our constituents.”

Sanders creates a bit of a problem for Democratic leadership, as he can be expected to be spending much of his time on the campaign trail and his politics are well to the left of much of the caucus.

But Sanders pointed to his post as ranking member and speculated he would be heavily involved, and last year managed to cut one of the biggest deals of the year — on veterans’ health care.

Like Murray, retiring Senate Appropriations Committee ranking member Barbara A. Mikulski, D-Md., who Van Hollen is hoping to replace in the Senate, has the confidence of Democratic leaders and rank and file.

“At this stage, the budget is done,” said Senate Budget member Sheldon Whitehouse, D-R.I. “So, the center of gravity on this is much more in the Appropriations Committee than it is in the Budget Committee. And given the threat of a presidential veto, the White House has taken a very strong interest in an overall spending deal. I think for that, it would ordinarily flow through the regular leadership.”

Democratic-leader-in-waiting Sen. Charles E. Schumer of New York, who sits on Finance, could take an active role as well, but deflected the notion he would be part of a summit and nodded towards Murray and Mikulski instead.

And, of course, there’s another appropriator — McConnell — who has cut a series of budget and tax deals since 2010 even while in the minority.

“Sen. McConnell would likely do that himself or designate someone else,” said Majority Whip John Cornyn, R-Texas.

McConnell has to worry about running the Senate and could lean on Budget Committee Chairman Michael B. Enzi, R-Wyo.

Finance Chairman Orrin G. Hatch, R-Utah, said he would expect the Finance Committee to play a limited role, other than having “to come up with the money,” naturally.

How the White House fits is also uncertain. White House Press Secretary Josh Earnest said the talks must be led by members of Congress, with White House input.

Direct efforts by Obama to cut budget deals have generally crashed and burned, notably in 2011, while smaller congressionally negotiated deals — think Ryan-Murray or the Pelosi-Boehner doc fix deal earlier this year — have had greater success.

Vice President Joseph R. Biden Jr. would, in theory, be a strong choice, for his deep ties to the Senate and relationship with McConnell.

But it’s unclear if he still has his party’s confidence in these types of negotiations following the fiscal cliff deal, which gave Republicans permanent tax cut extensions without ending the sequester caps, and especially while he is still recovering from the death of his son Beau Biden.

McConnell spokesman Don Stewart didn’t want to speculate on what’s next.

“I don’t have a prediction yet about what would happen if Democrats go through with their leaders’ threats to filibuster funding for American troops and their families,” he said in a statement.

Niels Lesniewski and Steven T. Dennis contributed to this report.

Related:

McConnell Cool to Budget Summit

Appropriations Bill Face Democratic Roadblock

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