Senate Republicans are going to war with each other over the upcoming Electoral College vote in Congress as lawmakers try to fill a post-Trump power vacuum.

The public infighting is putting a spotlight on simmering divisions and setting up the scenario Senate Majority Leader Mitch McConnell (R-Ky.) — who watched GOP squabbling cost him seats in previous election cycles — wanted to avoid when he warned members not to object to Wednesday’s counting of the electoral votes.

Instead, in a rare act of defiance, at least 13 Republican senators are supporting an effort to overturn the election results, offering a glimpse of what may lie ahead for a caucus with competing political ambitions heading into 2024.

“Members are going to act in their own interest quite often. You’ve got folks who want to run for president, so their priority is not necessarily the same as McConnell’s. You’ve got those who are scared to death of being primaried. ... Is that ideally what McConnell wanted? No, of course not,” said GOP strategist Doug Heye, former director of communications for the Republican National Committee.

Congress will hold a joint session Wednesday to count the Electoral College votes. At least 13 GOP senators and more than 100 House Republicans have endorsed challenging the election results in battleground states where President-elect Joe Biden defeated President Trump.

The president has publicly called out otherwise loyal Republicans who have voiced opposition to the effort.

“How can you certify an election when the numbers being certified are verifiably WRONG. ... Republicans have pluses & minuses, but one thing is sure, THEY NEVER FORGET!” Trump tweeted about longtime ally Sen. Tom Cotton (R-Ark.), a potential White House contender who is not backing the electoral objections.

In another tweet Monday, Trump predicted the “ ‘Surrender Caucus’ ... will go down in infamy,” in reference to GOP lawmakers not supporting efforts to overturn the election.

Trump’s tweets are the latest broadside he’s offered against Senate Republicans in recent weeks as many of them have acknowledged reality: Biden won the election and Wednesday will not change that.

The shots across the bow on Monday underscored how the quadrennial formality of counting the electoral votes has quickly become a televised loyalty test that is splintering not only the party’s potential White House contenders but also senators up for reelection next year.

“This is not healthy for the Republican Party,” said Sen. Ben Sasse (R-Neb.), a potential 2024 contender. “This is bad for the country and bad for the party.”

GOP Sens. Ron Johnson (Wis.), John Kennedy (La.) and James Lankford (Okla.) are each up for reelection and part of the gang of 11 that announced over the weekend that they would support challenging the election results absent a commission being formed to conduct a 10-day audit.

Meanwhile, Sen. Rob Portman (R-Ohio), who is up for reelection in 2022, became the latest to announce that he would not join that effort.

In addition to Portman, other in-cycle Republicans like Sens. Richard Shelby (Ala.), Roy Blunt (Mo.), and Lisa Murkowski (Alaska) have said they will oppose efforts to challenge the election results. Sens. Pat Toomey (R-Pa.), who is retiring, and Richard Burr (R-N.C.), who has previously said he wouldn’t run for reelection, are also opposed.

“I don’t think either of the two efforts has any chance for success, and I actually like to come up with plans that have a chance of being successful,” Blunt said.

Senate Republicans have gone through multiple rounds of public and private infighting as the decision to challenge the election results gained momentum in the conference.

After Toomey warned over the weekend that the effort by Sen. Josh Hawley (R-Mo.), Sen. Ted Cruz (R-Texas) and others “undermines” the “right of the people to elect their own leaders,” Hawley sent an email to the caucus arguing they should save the debate for Wednesday.

“Instead of debating this issue of election integrity by press release, conference call or e-mail, perhaps we could have a debate on the Senate floor for all of the American people to judge,” Hawley wrote.

Whether the GOP infighting will last beyond Wednesday is unclear.

Despite the current fight, McConnell, Trump and their allies have largely been united since January 2017. And with Biden taking office this month, Senate Republicans could unite against a Democratic White House and Democratic-controlled House, with GOP brawling taking a back seat.

“That should unify Senate Republicans. Whether all of them want to be unified is obviously an open question,” said Heye.

Scott Jennings, a former adviser to McConnell, warned against reading too much into the Electoral College fight but acknowledged that “as long as you have people out there that are running for president ... they’re going to do things from time to time that may not be aligned with what’s in the best interest of what their party leaders want them to do.”

This isn’t the first time McConnell has faced members with ambitions that are at odds with his strategy, which has consistently been to avoid making Republicans take tough votes as he tries to protect the caucus and their slim Senate majority.

In 2013, Cruz was at the center of a failed bid to repeal ObamaCare; in 2015, Sen. Rand Paul (R-Ky.) clashed with McConnell over surveillance programs; and Sens. Marco Rubio (R-Fla.) and Tom Cotton (R-Ark.) briefly agitated their colleagues when they hijacked the Senate floor during the debate on the Iran nuclear deal.

But unlike those fights, Wednesday’s votes are fueling concerns that defections could be used as primary fodder down the road, sparking unusually high-profile infighting among a caucus that McConnell has managed to keep relatively unified despite the chaos of the Trump era. Several newly elected senators, sworn in Sunday, are also backing the election challenges, which will be the Senate’s first votes of the 117th Congress.

“Each one of us has to make our best recommendation. The leader’s priority is always to keep the majority, and I respect that,” said Sen. Roger Marshall (R-Kan.), who supports challenging the results.

Asked about the discussion causing long-term divisions in the party, Sen. Susan Collins (R-Maine) urged her colleagues to “start acknowledging reality and working together.”

McConnell has not publicly commented on the decision by some of his members to challenge the election results, but he told the caucus last week that he viewed it as the “most consequential vote” of his congressional career and urged Republicans last month not to join a push by House conservatives to object.

Sen. John Thune (R-S.D.), McConnell’s No. 2, has predicted that efforts to challenge the election will go down like a “shot dog” but said that leadership isn’t leaning on members to vote against the objections. Because a challenge to a state’s Electoral College vote needs a majority of both chambers to be successful, the effort to overturn the results of even a single state is guaranteed to fail.

“We are letting people vote their conscience. This is an issue that’s incredibly consequential, incredibly rare historically and very precedent-setting,” Thune said. “Our members, this is a big vote, they are thinking about it. I think I know where things are headed but ... we’ll see what comes out.”