The flashpoint for the open hostilities is a bill that would provide two years of budget-making stability on the heels of one U.S. government shutdown and multiple debt-ceiling showdowns that risked damaging the American credit rating.
Tea party groups that hold considerable influence have castigated the legislation as a sellout of conservative principles, because it would moderate planned spending cuts previously scheduled under the so-called fiscal cliff.
Pressure from the grassroots, and conservative members, is nothing new to the Republican leaders in Congress. Only this time, they're fighting back against the party's own supporters — and they're doing it loudly.
The most resonant rhetorical blast came Thursday from House Speaker John Boehner. In past budget negotiations he'd shown reluctance to take on the Tea party base and, in fact, had even used their control over him as bargaining leverage, telling the White House and Democrats he couldn't offer any concessions or his members might desert him.
This week his patience appeared to run out when some people criticized the bipartisan budget bill even before it was made public.
"It's just that, you know, there just comes to a point when some people step over the line," Boehner told reporters Thursday. "When you criticize something and you have no idea what you're criticizing, it undermines your credibility."
Boehner blamed the same conservative groups for causing the temporary government shutdown this past fall. They had promoted the idea that government should be closed unless President Barack Obama's health plan was defunded. And many politicians fell into line, fearful of primary challenges from the right along with a loss of grassroots fundraising dollars and organizational muscle.
Looking back, Boehner said the pressure exerted over Republican law-makers forced them into a bad tactical place.
"Well, frankly, I think they're misleading their followers. I think they're pushing our members in places where they don't want to be. And frankly, I just think that they've lost all credibility," Boehner said of the groups.
"You know, they pushed into this fight to defund Obamacare and to shut down the government. Most of you know, my members know, that wasn't exactly the strategy that I had in mind. But if you recall, the day before the government reopened, one of the people that — one of these groups stood up and said, well, we never really thought it would work.
"Are you kidding me?"
One of the groups in question, Heritage Action, has said it will add the budget vote to its "scorecard" — its tracking of how congresspeople vote and how true they are to conservative principles.
It bemoaned the fact the U.S. federal budget would rise beyond $1 trillion, thanks to $63 billion in "tax" increases dressed up as a variety of user fees. The plan would restore about one-third of the "fiscal cliff" cuts and replace its across-the board spending reductions with more targeted measures.
"This is a significant achievement for President Obama, who believes that government spending is a panacea to America's economic woes," the Tea party-affiliated Heritage Action group said this week.
The threat didn't work. On Thursday, a crushing majority of members from both parties in the House of Representatives supported the bill, which will now move into the Senate.
Democrats, meanwhile, expressed hope that recent events might lead to a more productive U.S. political system. The current Congress is on track to perhaps become the least productive ever, in terms of bills passed.
They said they hoped Boehner might have become emboldened to work more often across party lines, instead of being beholden to his party's right wing. Nancy Pelosi, the Democratic minority leader in the House of Representatives, rattled off a list of bipartisan initiatives that might pass if Boehner is willing to brave the wrath of the right.
Immigration reform. Infrastructure. A bill seeking to end workplace discrimination against gays and lesbians. Background checks for gun purchases. Those were four examples she cited of legislation that might pass if Boehner chooses to work out bipartisan deals, instead of courting the right.
Pelosi declined to predict, however, whether this week's bipartisanship on the budget might be a one-off event or a real turning point for what has been dubbed the "do-nothing" Congress.
"I think it's neither. I don't think it's a one-off, and I don't think it's a great turning point," Pelosi told reporters on Capitol Hill.
"But I think that we have many more areas that we can work together in a bipartisan way."
The White House, for its part, has largely avoided getting drawn into this week's internal Republican family feud. But it has endorsed the budget legislation, which has yet to pass Congress.
"You could see the federal government go from being a drag to being a net positive if this (budget bill) goes through, which is hard to believe," Obama spokesman Jay Carney said at a press briefing Thursday.
"Now, that's a pretty unimpressive bar for Washington to clear, but it reflects that for too long now in shutting down the government, in refusing to compromise, Washington has actually caused problems for the economy, when at the very least it should be neutral.
"And at its best, which is what the president believes it ought to do, Washington should be taking action that helps the economy grow... And that's how it should be. And most importantly, perhaps psychologically, it tells the American people that, at least for the next couple of years, if Congress passes it, they don't have to worry about Republicans deciding the shut down the government again over their ideological disagreements with the president."