Confrontations between the parties, and factions within the GOP conference over government spending levels will probably leave Congress in gridlock in the weeks ahead, dragging to a halt the unusually rapid pace House and Senate appropriators have managed to set with their fiscal 2016 bills.

A breakthrough would come only if Republicans and Democrats are able to negotiate a new budget agreement later this year, though there’s been scant movement in that direction.

Recent filibuster threats by Senate Democrats, as well as the razor-thin margin by which the House passed a spending bill for transportation and housing programs last week, could portend a standstill in both chambers. But it’s unclear how long party leaders will continue to pursue fiscal 2016 work before they allow it to grind to a halt due to the larger disagreement over spending.

The tipping point could very well come in several days when Senate Democrats are expected to blockade the nearly $576 billion Defense spending bill, preventing the chamber from beginning debate on that — and effectively any other — appropriations measures.

Several lawmakers indicated such a standstill could not only halt floor work on Senate appropriations bills, but also slow House efforts.

Rep. José E. Serrano of New York, a senior Democratic appropriator, said Chairman Harold Rogers, R-Ky., “seems to want to get the bills through, but any time you have one body saying they’re not going to do anything then you’ll start to get people saying, ‘Why are we doing this? It’s not going to happen.’ We could lose momentum.”

Rep. Tom Cole, R-Okla., chairman of the Labor-HHS-Education Appropriations Subcommittee, said problems with last year’s fiscal 2015 bills were an example.

“We moved seven across the floor,” Cole said, “but when it was clear Democrats in the Senate weren’t going to pass a single bill, at that point you start losing floor time and you start asking yourself, ‘Do I really want to put my members through a series of tough votes under an open amendment procedure when the other body’s not moving?’ So there’s always that risk, but I would hope not.”

Contentious Bills Ahead

Meanwhile, work at the committee level will also get stickier in the House as Rogers begins to mark up the most contentious nondefense spending bills. That includes the titles that fund the Environmental Protection Agency, border control and Health and Human Services office that implements the 2010 health care law.

These are bills that party leaders in recent years have shied away from bringing to the floor due to their propensity for attracting highly partisan policy riders.

“It gets rougher now. It doesn’t get easier,” Serrano said. “It’s not like Defense where people feel like they have to vote for it. And the amendments will get nastier.”

Rogers indicated he will trudge along anyway.

“We’re going to proceed with our bills regardless and go as far as we can go,” he said.

Despite the very narrow margin by which the Transportation-HUD bill passed last week, Rogers said that experience doesn’t necessarily mean trouble for the other spending bills.

“Each bill has its own characteristics, and there were things in that bill that were unique to that bill that probably will not reoccur, but all bills are tough to pass,” he said.

But with the passage of the Defense appropriations bill last week, the committee has run out of relatively easy spending measures, and will face challenges shepherding the next two bills in the queue to passage: the $40.5 billion measure that funds foreign aid and embassy security and the $20.25 billion bill for the Treasury Department and the District of Columbia .

Pressure on Spending

Conservatives have indicated their votes will not be easy to win. Indeed, an announcement by Heritage Action urging members to vote against the Transportation-HUD bill earlier this month caused headaches for the GOP whip team.

“Right now, all of that pressure is coming from people who want to spend more,” said Dan Holler, spokesman for Heritage Action for America. “In our minds, the conservatives who would prefer to have lower spending caps than what we currently have are being taken for granted. The only way to reassert spending constraint into the conversation is for conservatives to begin flexing their muscles on these appropriations bills so that they’re not being taken for granted.”

Cole predicted “narrower” margins for nondefense spending bills in the weeks to come.

“Things are moving,” he said. “How much further it will go, I don’t know.”

Key members of both parties have indicated they are open to another budget deal that could end the appropriations standoff, but each side appears to be talking past the other.

Speaker John A. Boehner said last week that Obama hasn’t asked to negotiate a budget accord.

“If he wants to have a budget negotiation all he has to do is ask,” Boehner said. “I’m a pretty reasonable guy.”

White House Press Secretary Josh Earnest has said budget talks must be led by members of Congress, though with assistance from the White House.

Steven T. Dennis contributed to this report.