Political leaders are generally at their strongest the moment they take office.

Republican leader Kevin McCarthy is far from assured of winning sufficient support in his party to become House speaker next month. But even before the vote, his authority is already weakening by the day -- in a way that could make him a speaker who is in office but not in power.

The tiny GOP House majority that takes over in January, after a disappointing midterm performance, would mean a fragile governing mandate for any party at any point in American history. And the ideological struggle being waged by pro-Donald Trump extremists inside the party would have made even a more comfortable majority volatile.

But the compromises that McCarthy is facing in his increasingly bitter campaign for the speakership threaten to leave him as a tool of the most radical members of his conference and could diminish his capacity to hold the job in the long term.

The California Republican is fighting a rearguard battle against members who want to make it easier to eject a sitting speaker and he's appeasing ex-President Donald Trump's extremism and that of acolytes like Georgia Rep. Marjorie Taylor Greene to save a narrow political power base propping up his dream of running the House.

Once an avuncular and smooth-talking GOP rising star, McCarthy has adopted some of the confrontational defiance of the Make America Great Again movement, seeming to seek out soundbite clashes with the press as badges of honor.

Given that he can only afford to lose four votes to be elected speaker -- and then to pass legislation -- it would take a political genius to corral the GOP conference. While McCarthy is broadly popular among Republican lawmakers and is a prodigious fundraiser, nothing so far in his career suggests he is a leader of that caliber. In fact, he seems less of a heavyweight than former GOP Speakers John Boehner and Paul Ryan, who were driven out of politics by the impossibility of running a riotous Republican majority.

If politics is the art of the possible, McCarthy is acting in a way that is most likely to allow him to reach power -- even if the speaker's gavel might turn into a poisoned chalice and require him to infringe democratic values to keep it.

But his struggle to lock in the speakership and his possible futile future mission of amassing a governing majority amount to more than an inside-Washington brouhaha or internal GOP feud. If the House cannot pass spending bills, or if radical members of the Republican conference try to hold McCarthy hostage, the economic and social consequences could soon affect tens of millions of Americans. Government shutdowns, budget showdowns and an impasse over raising US borrowing limits could severely damage the US economy, the military's readiness and the dollar's reputation as a reserve currency.

This is one reason why the current year-end tussle over whether to fund the government for a full year -- a bipartisan framework agreement for which was announced Tuesday night -- or for just a few months is so critical since it could dump a fiscal crisis on the lap of a weak and easily manipulated new speaker next month.

McCarthy's impossible math

From a broader political perspective, it might be in McCarthy's interest to stand up to the most extreme members of his conference. The path to the GOP majority went through comparatively moderate seats in places like New York that will be most at risk in the 2024 election. And pro-Trump election-denying extremists, like those who are tormenting him now, were mostly rejected by swing-state voters in the midterm elections. The anti-Trump vote was also decisive in the 2018 election when Republicans lost the House and in 2020 when they lost the presidency.

So showing voters in 2024 that GOP governance addressed key problems like inflation and the economy will be important. But while he has announced he will form a select committee to examine China's growing threat, which could unite both parties, most of McCarthy's recent rhetoric has focused on a relentless set of investigations of the Biden administration and conservatives' interest in impeaching Homeland Security Secretary Alejandro Mayorkas.

The GOP leader's attitude is easily explained. The nature of the House, with its two-year terms and gerrymandered districts, means McCarthy's lawmakers are easily radicalized, with the greatest threat to their jobs often coming from more extreme opponents in primaries. And while he is clearly catering to the most zealous members of his conference, the House GOP as a whole is extremely conservative. Two years ago, a majority of Republican lawmakers, including McCarthy, voted against certifying Joe Biden's election win, despite the absence of any credible claims of fraud and after the desecration of Congress by Trump's mob.

The steps McCarthy is taking to try to secure the speakership -- and the future complications that may entail -- were evident on Tuesday when he gave Greene, the Georgia Republican, a pass for her latest effort to mock the trauma of the Capitol insurrection. The congresswoman had said over the weekend that had she been in charge on January 6, 2021, the riot would have succeeded and the mob would have been armed. She later insisted she was being sarcastic after the White House complained her comments were a slap in the face to law enforcement and against fundamental US values.

Asked by CNN's Manu Raju on Tuesday about Greene's latest inflammatory comments, McCarthy shrugged them off: Oh, I think she said she was being facetious, the possible future speaker answered. His attitude was not a surprise; it was consistent with his attempts to rewrite the history of the worst attack on US democracy in modern times, for which he briefly said Trump bore responsibility.

But it also reflected Greene's growing personal power, after she broke with some radical GOP members and lined up to support McCarthy's speakership. After coming to Congress as a fringe figure, and quickly losing her committee assignments over her past retweets of violent rhetoric against Democrats, Greene now promises to be one of the most prominent faces of the new GOP majority. That she has the latitude to make what to many people are offensive and insurrectionist comments without any fear of rebuke from her party's leader says a lot about her position. And it also shows that while Trump's power may be waning elsewhere after a lackluster launch of his 2024 campaign, his influence over his followers in the House, like Greene, remains strong.

The same dynamic was at play when McCarthy declined to directly criticize the ex-president for meeting with white supremacist Nick Fuentes at a dinner also featuring Kanye West, the rapper now known as Ye, who has recently made a string of antisemitic remarks. In a histrionic performance at the White House after meeting Biden and other congressional leaders last month, the House Republican leader falsely claimed that Trump had condemned Fuentes four times, when he hadn't done so once.

How the current spending fight is being shaped by McCarthy's speaker bid

McCarthy's hardening opposition towards a year-end spending bill in the lame duck Congress also shows that he understands that without indulging his most ideological colleagues, he may never become speaker.

CNN's Raju and Melanie Zanona reported Tuesday that McCarthy had signaled at the White House meeting that he'd be open to a large bill. But while Senate Republican leader Mitch McConnell worked on such a measure Tuesday and declared it broadly appealing, McCarthy told his members that he was a Hell no on the measure.

The split not only augurs likely future tensions between Republicans in the House and McConnell, it raises the possibility that it will become politically more difficult for some Republican senators to vote for a spending deal now -- especially as conservative media has taken up McCarthy's line.

A short-term fix that takes the issue into early next year could provoke a gargantuan showdown with the White House in the first days of GOP control of the House, with members firmly committed to slashing Biden's spending plans and domestic agenda. Even though that would be a high risk for McCarthy that could backfire with a national electorate, setting up the possibility of such a confrontation might be one way to shore up his vote in the speakership campaign.

Still, given that Democrats should be able to pass a broader funding deal in the final days of their majority, McCarthy's opposition could win him points with no long-term consequence -- a potentially useful political situation. This became more likely on Tuesday when Senate Republicans and Democrats and House Democrats announced the framework agreement on an omnibus appropriations bill.

One thing the California Republican does have going for his dreams of the top job is the fact that there so far is not a strong alternative to his candidacy. GOP Rep. Andy Biggs of Arizona, the former head of the Freedom Caucus, has launched a long-shot bid.

But McCarthy faces a nervous holiday season.

On Tuesday, Raju asked him to comment on a claim by Florida Republican Rep. Matt Gaetz that he will never hit the 218-vote threshold.

Do you believe Gaetz or do you believe me? he replied.

That there is even a question over whether the words of the supposedly most powerful Republican-to-be in Washington or a renegade member carry more currency reflects McCarthy's diminished authority -- and highlights the risk that if he does have a speakership, it could be a weak one.