WASHINGTON – Rep. Kevin McCarthy's bid to become speaker remained in peril Monday as he toiled to break through the entrenched opposition of hard-right lawmakers and unite his fractious majority, with just hours to go before Republicans assume control of the House of Representatives.

The refusal of ultraconservative lawmakers to embrace McCarthy, R-Calif., even after he made a key concession that would weaken his power in the top post, threatened a tumultuous start to GOP rule in the House. The standoff underscored McCarthy's precarious position within his conference and all but guaranteed that even if he eked out a victory, he would be a diminished figure beholden to an empowered right flank.

In a vote planned for around midday Tuesday, when the new Congress convenes, McCarthy would need to win a majority of those present and voting — 218 if every member of the House were to attend and cast a vote. But despite a grueling weekslong lobbying effort, McCarthy appeared short of the near-unanimity he would need within his ranks to prevail.

A group of five Republicans has publicly vowed to vote against him, and more are quietly opposed or on the fence. Republicans are poised to control 222 seats and Democrats are all but certain to oppose him en masse, so McCarthy could afford to lose only a handful of members of his party.

With little time left before the vote, McCarthy worked into the evening in the Capitol on Monday to try to lock down the votes, and some allies projected optimism that he could yet close the gap.

"I think we can get there," Rep. Jim Jordan of Ohio told reporters as he left a meeting in McCarthy's office Monday night.

The haggling continued even after McCarthy had tried over the weekend to win over the hard-liners with a major concession, by agreeing to a rule that would allow a snap vote at any time to oust the speaker.

Lawmakers opposing him had listed the change as one of their top demands, and McCarthy had earlier refused to swallow it, regarding it as tantamount to signing the death warrant for his speakership in advance. But in recent days, he signaled he would accept it if the threshold for calling such a vote were five lawmakers rather than a single member.

That was evidently not enough to sway the five rebels opposing him, and more dissenters emerged Sunday night, after McCarthy announced the concession in a conference call with House Republicans.

With the holdouts unwilling to bend, McCarthy could not tell lawmakers and members-elect during the call that he had secured the votes for speaker. McCarthy could only say that he still had time before the vote Tuesday, according to two people familiar with the discussion who insisted on anonymity to describe it.

Roughly two hours later, a separate group of nine conservative lawmakers — most of whom had previously expressed skepticism about McCarthy's bid for speaker — derided his efforts to appease their flank of the party as "almost impossibly late to address continued deficiencies." The group included Reps. Scott Perry of Pennsylvania, chair of the Freedom Caucus, and Chip Roy of Texas.

"The times call for radical departure from the status quo — not a continuation of past, and ongoing Republican failures," the group said in a statement. "For someone with a 14-year presence in senior House Republican leadership, Mr. McCarthy bears squarely the burden to correct the dysfunction he now explicitly admits across that long tenure."

The pile-on continued later Monday, when the Club for Growth, the conservative anti-tax group, effectively threatened to punish Republicans who embraced a McCarthy speakership. The group announced that it would downgrade its public ratings of lawmakers who voted for any candidate who refused to return to the House rules in place in 2015, which allowed for the snap vote of no-confidence that drove out Speaker John Boehner, R-Ohio.

The group also demanded that the next speaker bar the leading House Republican super PAC from spending money in open party primaries. That demand reflected a top grievance of conservative hard-liners in the House who are irate that McCarthy has used the committee to back more mainstream candidates.

McCarthy has pledged to fight for the speakership on the House floor until the very end, even if it requires lawmakers to vote more than once, a prospect that now appears to be a distinct possibility. If he were fail to win a majority Tuesday, members would take successive votes until someone — McCarthy or a different nominee — secured enough supporters to prevail.

That could prompt chaos not seen on the House floor in a century. Every speaker since 1923 has been able to clinch the gavel after just one vote.

Asked on Monday evening how many ballots it would take for McCarthy to prevail, Jordan replied, "We'll see tomorrow."

He brushed off the threat of a messy floor fight that might take multiple ballots to resolve, telling reporters, "I think America will survive."

No viable candidate has yet stepped forward to challenge McCarthy, and it was not clear who would be able to draw enough support if he proved unable to do so. Potential alternatives who could emerge if he fails to secure enough votes include Rep. Steve Scalise of Louisiana, his No. 2; Jordan, a onetime rival who has strong support among the powerful ultraconservative faction; and Rep. Patrick McHenry of North Carolina, one of his close advisers.

Laboring to avoid a scene and cement the speakership, McCarthy has made a number of concessions over the past few months in attempts to lock up votes of far-right members.

He unveiled a package of rules on Sunday night governing how the House operates that included several demands issued by members of the Freedom Caucus, such as the adoption of the so-called Holman rule, which allows lawmakers to use spending bills to defund specific programs and fire federal officials or reduce their pay.

The proposed rules would also end proxy voting and remote committee hearings, practices Democrats began in response to the pandemic, and create a new select subcommittee under the Judiciary Committee focused on the "weaponization" of the federal government.

The package could also hamstring the Office of Congressional Ethics, which undertakes bipartisan inquires about lawmakers' conduct and makes recommendations for discipline to the Ethics Committee. One proposed change would impose term limits for board members, which would result in the removal of all but one Democrat as the panel considers whether to begin an inquiry into certain Republican members of Congress over their conduct related to the Jan. 6, 2021, attack on the Capitol.

Another proposal would mandate that the office hire investigators within the first 30 days of a new Congress, a requirement some ethics experts fear could leave the office understaffed for lengthy periods if hires are not made within that time frame.

McCarthy has also called for a "Church-style investigation" into past abuses of power by the FBI and CIA, a reference to the select committee established in 1975, informally known by the name of the senator who led it, Frank Church of Idaho, that looked into abuses by U.S. intelligence agencies.

He toughened his language in response to hard-right demands to oust Alejandro Mayorkas, the homeland security secretary, calling on him to resign or face potential impeachment proceedings. He promised Rep. Marjorie Taylor Greene of Georgia, who was stripped of her committee assignments for making a series of violent and conspiratorial social media posts before she was elected, a spot on the coveted Oversight Committee.

McCarthy threatened to investigate the House select committee looking into the Jan. 6 attack, promising to hold public hearings scrutinizing the security breakdowns that occurred. Last month, he publicly encouraged his members to vote against the lame-duck spending bill to fund the government.

It is unclear whether any single offering from McCarthy at this point would be enough to win over some lawmakers.

During the call Sunday, Rep.-elect Mike Lawler of New York, who has announced his support for McCarthy, pointedly asked Rep. Matt Gaetz of Florida, a ringleader of the opposition, whether he would vote for McCarthy if the leader agreed to lower the threshold for a vote to oust the speaker to just one member of Congress. Gaetz was noncommittal, according to a person on the call who recounted it on the condition of anonymity.

The exchange underscored the challenge McCarthy faces in trying to keep control of the House Republican Conference, which includes the task of bargaining with a group of lawmakers who practice a brand of obstructionism that Boehner famously described as "legislative terrorism."