As shocking as it was to watch Bob Corker publicly state what many in Congress have presumably been thinking of Donald Trump for months, three days after the Tennessee senator’s scorched-earth interview with The New York Times, his Republican colleagues are desperate to move on. “I would encourage them both to stop what they’re doing and get focused on what we need to be doing,” Sen. Roy Blunt told Politico shortly after Trump tweeted a schoolyard insult at “Liddle‘ Corker.” His Iowa counterpart, Joni Ernst, echoed Blunt’s sentiment: Trump “needs to stop. But I wish Bob would stop too.” She added: “I would hope that it doesn’t bleed into legislation.”

Trump’s feud with Corker is hardly the only distraction threatening to tank the G.O.P. agenda. In the last few months, the president has seemed increasingly agitated and distracted, wasting his time lashing out at professional athletes on Twitter while initially ignoring a worsening humanitarian crisis in Puerto Rico. He has careened from resentment over losing an electoral proxy war in Alabama’s Senate primary, where he backed the establishment candidate, to fury over a series of news reports detailing how his secretary of state, Rex Tillerson, allegedly called him a “moron.”

The fear echoing across Capitol Hill is that the Trump-Corker spat will now cripple Republicans’ attempt to pass a major tax-reform bill in the next several months. After their spectacular failure to repeal and replace Obamacare—a goal they strove toward for seven years—and with the prospect of Steve Bannon building an army of far-right goons to challenge them in the midterm primaries, Republicans seem desperate to develop some form of consensus. “This is not one that can get left on the cutting-room floor,” Josh Holmes, a communications adviser with ties to Mitch McConnell, told the Times. “It has become a barometer of whether Republicans can govern under Trump’s leadership.”

A high-profile feud between the president and Congress doesn’t help, and with the Republicans only holding a two-seat majority in the Senate, the possibility of Corker abandoning them, on any bill, is daunting. “Defeating the budget is dishing more punishment on your colleagues than it is on the president,” said Neil Bradley, a senior official at the Chamber of Commerce.

No one is feeling the pain more acutely than McConnell, whom Trump takes a perverse glee in undermining. Under mounting pressure to pass a bill now considered a litmus test, the Senate leader published an op-ed on NBC News’s Web site that all but begged Democrats to vote for his tax-reform plan. “Democrats are under pressure from the left to oppose just about everything President Donald Trump touches—even ideas they themselves used to promote,” he wrote, requesting that they put their antagonism aside to, at the very least, get something done. For McConnell to directly appeal to the Democrats—even if it means scraping only one vote from their caucus—speaks to the precariousness of the Republicans’ position: how can they keep pushing their agenda when losing one vote could doom it?