Kevin McCarthy has already moved into the speaker’s office, even as an influential conservative group urges members to vote against him unless he concedes to key rules changes.

With the House slated to start voting on who will command the gavel in less than 24 hours, McCarthy remains short of the necessary 218 votes. And his last-ditch efforts, including a long list of concessions he released to his conference over the weekend, has done little to sway his most ardent detractors.

And even as McCarthy predicted concessions he made to the House rules are helping him pick up support, his opponents and skeptics spent Monday lobbing new criticisms his way.

“Why didn’t we get McCarthy’s proposed rules package at least 72 hours in advance?” tweeted Rep. Dan Bishop (R-N.C.), a Freedom Caucus member.

Electing a speaker is typically a symbolic moment, with the vote decided weeks if not months ahead of time. But absent a sudden flip among his detractors, McCarthy’s bid for the gavel will prompt a historically rare showdown, marking just the second time since the Civil War that the race could go beyond one ballot. In fact, many Republicans are bracing for votes that could last multiple days, as McCarthy’s allies vow to only vote for him and five conservatives promise to oppose him, with no clear alternative candidate.

The conservative Club for Growth released a whip notice for the speakership vote on Monday, urging a no vote on McCarthy — without explicitly naming him — if he didn’t concede to various rules being pushed by some of those opposing him, many of them members of the House Freedom Caucus.

Those lawmakers’ demands have included allowing any one member to force a vote on the House floor to depose a speaker. The Club for Growth also mirrored those members’ calls for prohibiting the Congressional Leadership Fund, a campaign committee closely aligned with McCarthy, from “spending money or providing grants to any Super PAC to engage … in open Republican primaries or against any Republican incumbent.” The group also took issue with the lack of « true conservatives » being represented in leadership.

McCarthy convened a strategy session on Monday evening with dozens of his supporters. Rep. Jim Jordan (R-Ohio) characterized the meeting as aimed at helping the California Republican ahead of Tuesday’s vote. One of McCarthy’s most dug-in opponents, Rep. Matt Gaetz (R-Fla.) was also spotted entering McCarthy’s office with Rep. Scott Perry (R-Pa.), chair of the House Freedom Caucus, and Rep. Lauren Boebert (R-Colo.), neither of whom have committed to voting for the Californian for speaker.

Despite not yet having a lock on the gavel, McCarthy is spending Monday working out of the speaker’s office, a tradition routinely granted to the speaker-elect. If he falls short, he would have to move back out of the prestigious office.

Republicans are preparing for a long day Tuesday. Rep. Kelly Armstrong (R-N.D.), a McCarthy ally, predicted Republicans will go “however long it takes.” But the first vote would provide some early indications on how the day would play out, he added.

“The way the alphabet works, you’ll know on the first ballot pretty quickly. And then we’ll figure out how it grinds out,” Armstrong said, referring to the alphabetical process for calling on members to cast their votes.

Meanwhile, Rep. Andy Biggs (R-Ariz.), who McCarthy opponents are backing as a figurehead for their frustration, described the Californian as being in “total bargaining mode” but that he doesn’t believe McCarthy “will ever get to 218 votes.”

Others issued more cryptic takes: “Some people who run campaigns against the swamp sure are quick to wilt in the face of challenges (to different degrees) to that very swamp…” tweeted Rep. Chip Roy (R-Texas) on Monday.

But as McCarthy’s opponents take a hard line, some of his supporters are reviving their own threats.

McCarthy ally Rep. Don Bacon (R-Neb.) said Monday his previous warning — that a band of moderate Republicans would work with Democrats to elect a centrist GOP speaker, if conservatives tank McCarthy — remains on the table.

“If a few won’t be part of the 218 members we need to govern, we’ll then find other ways to get to 218,” Bacon wrote in an op-ed in the Daily Caller.