For McConnell, the conservative rebellion over vaccine mandates is yet another challenge to band his 50 members together and avert catastrophe. A second one awaits around the corner as a potential U.S. credit default looms later this month. McConnell has vowed there will be no shutdown and no default; both may depend to on whether he can rein in all of his members.

Sen. Cynthia Lummis (R-Wyo.), who’s as conservative as they come, said that while she wants to defund vaccine mandates, she’s going to trust McConnell to shape the party’s strategy.

“My gut tells me, let leadership do the best they can and trust them,” Lummis said. “I just am going to trust the people who are leading and negotiating … that’s how flexible I’m willing to be.”

With the pandemic still clouding everyday life nationwide, many Republicans believe a shutdown over vaccine mandates will reflect poorly on their party and argue there are way better ways to make their point. Sen. Mike Braun (R-Ind.) wants to channel the GOP frustration with required vaccinations into a vote next week to roll back President Joe Biden’s mandate. That would avoid his party taking the hit for a shutdown, even if it’s a short one.

“Most everybody agrees with me,” Braun said. “Almost everybody.”

During Wednesday’s Republican lunch, Lee argued that defunding the vaccine mandate through a government spending bill is the most effective way to make his point, according to one attendee. Lee seemed dug in and declined to comment afterward.

Inside the room, however, the Lee-led meeting was “lively,” as Braun put it. The Indianan must recruit at least one Democrat to join his separate vaccine-mandate rollback effort, and even if he does and it somehow passes the House, Biden can still veto it. Some conservatives see pushing for the defunding mechanism in a spending bill as a more effective option.

“There was not full agreement, that’s for sure,” said Sen. Roy Blunt (R-Mo.) after the lunch. “Shutdowns almost never work out.”

In some ways, the end result of this week’s shutdown clash may be out of McConnell’s hands. At this point, any one senator has the power to push government funding past the Friday deadline, and Lee has several allies who do not want to easily sign off on funding the government without concessions on the vaccine mandate. Those like-minded conservatives include Sens. Ted Cruz (R-Texas), Ron Johnson (R-Wis.) and Roger Marshall (R-Kan.).

“It’s up to Sen. Schumer. If he’ll stop any type of funding for the vaccine mandate, then I think this goes forward. But if he doesn’t?” Marshall said. “The folks back home want to know how hard we’re fighting for them.”

Still, Cruz and Marshall signaled they could accept an amendment vote on vaccine mandates if McConnell can secure one from Schumer, albeit at a 51-vote threshold instead of the usual 60-vote threshold. They hope they can peel away Sen. Joe Manchin (D-W.Va.), who opposed a similar push in September. Even then it’s highly unlikely Biden would ever sign such a bill.

With that in mind, several Senate Republicans are panning their colleagues’ strategy of forcing a shutdown fight over the issue, hoping conservatives back off before the midnight Friday deadline. McConnell ally Sen. John Cornyn (R-Texas) said he believed Republicans “have a lot of options short of blocking” a stopgap spending bill.

In fact, most Republican senators, from leadership allies to conservative stalwarts, said they do not support flirting with a shutdown over vaccinations. They say there are better ways to deal with it: Keep counting on the courts to block the mandate, push for amendment votes or try to wind down regulations through the Congressional Review Act.

Republicans said Wednesday that only a handful of their colleagues support what Lee is proposing. Still, the House Freedom Caucus leaned on the GOP leader on Wednesday “to deny timely passage of the CR unless it prohibits funding — in all respects — for the vaccine mandates.”

As he entered lunch, McConnell predicted that Republicans would end up “OK.”

“I just don’t quite understand the strategy or the play of leverage for a mandate that’s been stayed by 10 courts,” said Sen. Kevin Cramer (R-N.D.). “I want the vaccine mandates lifted, but I don’t think the [spending bill] is the tool to do it. For all practical purposes, the mandates weaken every single day.”

All 50 GOP senators currently support rolling back Biden’s mandates, and there’s clearly plenty of outrage within the party over them. The skepticism lies is over whether it should be a condition of funding the government. The Lee-backed strategy is reminiscent of the party’s ineffective approach to defunding Obamacare in 2013, which resulted in a lengthy shutdown and did not take down the law.

Many senators who support various efforts to strike down the vaccine mandates said risking a shutdown is a bridge too far: “It only takes one. I won’t be that one,” said Sen. Tommy Tuberville (R-Ala.).

“We don’t need to shut the government down. And we’re not going to have to do that. It’s just all talk,” Tuberville said in an interview. “Federal judges now have knocked down the mandates. That’s what we’re wanting to do. We’re wanting to do it the right way.”

Still, some in the GOP are beginning to steel themselves for a lengthy fight. The House still hasn’t passed a short-term funding bill, meaning that passage of any stopgap solution will come down to the wire. That could result in a brief shutdown over the weekend, at the hands of a klatsch of Republicans trying to make a point about vaccines.

“We’re going to go through this drama. We’re going to fund the government, we may have a structural shutdown over the weekend and then we’ll solve the problem. It’s great for a news cycle, but it eventually fixes itself,” said Sen. Thom Tillis (R-N.C.).

Tillis, who pointedly criticized Sen. Rand Paul (R-Ky.) for an ephemeral shutdown in 2018, added that “everybody — I don’t care if you’re talking about Schumer or Leader McConnell — we want to fund the government.”

Marianne LeVine contributed to this report.