WASHINGTON — The looming fight in the US Congress over a Supreme Court nominee threatens to doom the chances for a Republican budget and tangle Congress in appropriations gridlock.

The expected impasse over replacing the late Justice Antonin Scalia is endangering the plans of House and Senate Republican leaders who have repeatedly vowed to complete the full appropriations process and restore "regular order" to Congress. Ahead of the elections, Senate Majority Leader Mitch McConnell, R-Ky., intended to redeem the party's obstructionist reputation, but Democrats angered by McConnell's vow to block any White House nominee, may thwart those plans.

"Basically you infuriated and united Democrats on the one thing that was important to McConnell at this point: appropriations," said longtime Washington-based budget analyst Stan Collender. "The Republican leader has been saying we're going to show everybody we can make the trains run on time in Washington ... Now the Democrats are basically saying, if you're going to to be unreasonable about a Supreme Court nominee, we're going to make your life difficult on appropriations.'"

Prior to Scalia's death Feb. 13, House Speaker Paul Ryan, R-Wis., was working to wrangle members of the conservative Freedom Caucus to back a budget that would hew to the top lines of last year's Bipartisan Budget Act. Citing projections of a $19 trillion national debt and spiking deficit, its members have demanded a $30 billion cut to comply with statutory budget caps eased by a deal they never supported.

Yet it had looked as though like the 12 appropriations bills, in line with the deal’s numbers, would move smoothly through Congress with a combination of Republican and Democratic support — despite this year’s abbreviated calendar, according to Collender.

That changed when McConnell, after the first public confirmation of Scalia's death had died, said the GOP-controlled Senate would block consideration of President Barack Obama’s nominee to succeed him.

If McConnell blocks hearings, he invites retribution from Democrats., and i If he holds hearings, he invites condemnation from conservative groups, which have warned the GOP must not allow Obama’s nominee to proceed.

"Senator McConnell is right, under no circumstance should the Republican Senate majority confirm a Supreme Court nominee as Americans are in the midst of picking the next president," came a statement from Heritage Action for America.

While Senate Democrats have not signaled overtly they plan to extract retribution on Republicans, they are expected to do so through delay tactics, by offering copious amendments or filibustering procedural votes on Republican-backed appropriations bills expected as soon as early April. 

"It can go on forever, and if GOP leadership tried to get out an omnibus or continuing resolution in July, before Congress broke for the summer, there's no way the Democrats would agree to it, no matter what spending levels are in it," said Collender, now executive vice president at Qorvis MSLGroup.

In the House, Ryan, like McConnell, must now grapple with enraged, unified Democrats, who can no longer be relied upon to pass a budget resolution. If Ryan passes a leaner budget with the help of the Freedom Caucus and without Democrats, it faces likely rejection in the Senate, and it's unclear whether he can even do that.

After a closed-door meeting of the House GOP conference Feb. 12, Freedom Caucus chairman Rep. Jim Jordan would not say what sweetener would win his support for a Bipartisan Budget Act-compliant budget. His voting bloc is as yet undecided, he said after the meeting.

"In my mind, we are making this way too complicated," Jordan, R-Ohio, told reporters. "Do a budget that reflects conservative principals, send it to the Senate and do our job."

Complicating matters is the anti-establishment current in the presidential campaign that may be hemming in House Republicans who would otherwise adhere to the deal.

"You can see it through the presidential election that people are angry, they're frustrated, they're scared, and they don't trust Washington because there have been a lot of promises made that haven't been kept," said Freedom Caucus member Rep. Barry Laudermilk, R-Ga. "We have to show that we're going to keep promises that we make. The people definitely influence our decisions."

There is opposing pressure from defense hawks to add as much as $23 billion to defense through the wartime overseas contingency operations (OCO) account, led by House Armed Services Chairman Mac Thornberry, R-Texas. It was unclear after the GOP conference how Ryan would address this bloc.

"Stay tuned," said the chairman of the House Appropriations Defense subcommittee, Rep. Rodney Frelinghuysen, R-N.J. "I don't know. The speaker has been meeting with every conceivable group and clique out there."

A defense hike would be politically tricky because key Democrats have said they would demand parity on the non-defense side, a path that would surely be a deal-killer for fiscal hawks.

Sen. Barbara Mikulski, D-Md., the senior Democrat on the Senate Appropriations Committee and a key player in negotiating last year's budget deal, questioned the House GOP's attempt to raise OCO spending.

"It depends on what they mean and if they intend to keep the sense of parity between defense and domestic [spending]," Mikulski said of Republican arguments to increase OCO. "I'm not saying I'm for this OCO thing. Right now, while we also have to defend against terrorism, which I understand and support ... there are many threats to the United States that we pay for out of domestic spending — so parity, parity, parity."

House Budget Committee Chairman Tom Price, R-Ga., indicated his committee will begin marking up a budget proposal after Congress returns from recess Feb. 22. When asked about an increase for defense, he demurred.

"We're having conversations with every portion of the conference, and Chairman Thornberry and I have had extensive conversations about that," Price said.

Twitter: @reporterjoe