ATLANTA — Even ahead of President Donald Trump’s Georgia rally this weekend for two Republican senators, his part in their crucial runoff elections has been dominant and destabilizing — a harbinger of his likely role in the Republican Party after he leaves office.

Republicans see Trump as an essential turnout booster in the hard-fought Georgia contest next month, which will decide which party controls the Senate. But his unsubstantiated rants about election fraud and his attacks on GOP leaders in the state, which he lost to Joe Biden, have made it more difficult for Republicans to secure victory.

The tumult in Georgia is a preview of the uncharted political territory Republicans face after Trump’s presidency ends. In unprecedented fashion, the defeated but not conceding president is expected to remain front and center in his party. His erratic, lone-wolf style presents Republicans in Georgia and beyond with a dilemma like a spouse in a soured marriage: Can’t live with him, can’t live without him.

At issue are the two Jan. 5 Senate runoff elections, which pit Republican Sens. David Perdue and Kelly Loeffler against Democrats Jon Ossoff and Raphael Warnock, respectively. If Democrats win both seats, they will secure control of a 50-50 Senate, with Vice President Kamala Harris as a tiebreaker.

Some Republicans are warning Trump that his allegations of fraud in last month’s election — outlined again at great length Wednesday in a Facebook video he posted — could backfire by depressing turnout among Trump supporters in Georgia, risking loss of the party’s Senate majority, and ending his term on a divisive, defensive note.

“Any chance that Trump is going to have a positive legacy from his four years could potentially be tarnished by his continuing whining and complaining and incessant false accusations that the election was stolen from him,” said Allen Peake, a former Georgia Republican state representative from Macon.

But just as party unity is needed, Trump’s rhetoric has driven a wedge within the GOP. He has disavowed his past support for Georgia’s governor, Brian Kemp, and berated the secretary of state, because the two Republicans did not overturn his election loss. His tirades against the state’s GOP-run voting system have incited some supporters to threaten violence against election officials.

“Mr. President, you have not condemned these actions or this language,” said a furious Gabriel Sterling, a Republican state election official, at a news conference Tuesday. “This has to stop. We need you to step up — and if you’re going to take a position of leadership, show some!” He warned that people could be killed.

Trump’s campaign responded with a statement that condemned violence. But the president continued to denigrate Kemp and Secretary of State Brad Raffensperger on Twitter, saying: “Rigged Election. Show signatures and envelopes. Expose the massive voter fraud in Georgia. What is Secretary of State and @BrianKempGA afraid of. They know what we’ll find!!!”

Republicans are urging Trump to leave his grievances behind when he comes to Georgia on Saturday, and to deliver a concise get-out-the-vote message to supporters: Turn out for Loeffler and Perdue to keep the Senate as the last bastion of Republican control in Washington.

But within party circles there is fear Trump will continue pounding his divisive criticism. One hurdle: Republicans can’t effectively cast the Senate as Republicans’ last power center if Trump won’t acknowledge that he has lost the White House.

“I hope he can have a unifying message that entails focusing his fire on the Democrats, not the state’s Republican leadership,” said Brian Robinson, a GOP strategist who advised former Gov. Nathan Deal.

Trump is joining a battle that has already engaged Republicans and Democrats across the country because so much hinges on the outcome — whether President-elect Biden has a divided government, which will determine how hard it will be to move his agenda and nominations, and whether Trump emerges from the race with credit or blame for the result, his standing in his party either enhanced or damaged.

The scene in Georgia underscores how much Trump has dominated and changed the party. He is often at odds with establishment party leaders, has not been afraid to put his personal interest above the party’s, and his base is loyal to him, not to the traditional GOP.

Some Trump critics see his mission in Georgia as repairing a problem of his own making: the signs that some Republican voters are discouraged about participating — conservatives by his claims that Georgia’s voting system is rigged, and more traditional Republicans by his refusal to concede.

“The seats are in danger largely because of Donald Trump, and Donald Trump is also the only person who can save them at this point,” said Brendan Buck, a Republican strategist who was an aide to former House Speaker Paul D. Ryan (R-Wis.).

Some conservatives have been taking Trump at his word and urging Georgians to boycott what they call a rigged election.

L. Lin Wood, a Georgia lawyer, urged hundreds at a rally Wednesday in Alpharetta not to vote unless Loeffler and Perdue persuaded Kemp to call a special session to reform the election system.

“Why would you go back and vote in another rigged election?” he said. ” … You’ve got to fix it before we’ll do it again.”

Other Republicans have been countering that message. At a recent campaign stop in Marietta, Republican National Committee Chair Ronna McDaniel was asked by a voter why Republicans should worry about the runoff elections when the outcome is decided.

“It’s not decided!” McDaniel responded. ” … If you lose your faith and you don’t vote and people walk away — that will decide it.”

More than a dozen of Georgia’s most prominent Republicans, including former Gov. Deal and former U.S. Sen. Johnny Isakson, wrote a letter Wednesday calling for the GOP to not be distracted by the outcry over election fraud.

“We have watched with increasing concern as the debate surrounding the state’s electoral system has made some within our Party consider whether voting in the coming run-off election matters,” they wrote. ” … Now is the time to unite our Party and win these U.S. Senate seats.”

Allies of the president’s son Donald Trump Jr. set up a new super PAC to reach Trump voters in Georgia. The PAC, Save the U.S. Senate, is running a radio ad featuring Trump Jr. saying, “On Jan 5., the U.S. Senate is on the line and my father’s accomplishments are on your ballot.”

The effort addresses a long-term challenge for the party: Trump’s base includes many who are not regular GOP voters. Without him on the ballot, will they fall off? Trump has made clear he aspires to have a continuing role in the party, even suggesting he will run for president again in 2024.

“It’s become more clear, not less clear, that Trump is the center of the universe in the Republican Party and wields more influence than anyone else, times 100, within the party,” said Andy Surabian, a co-founder of the new PAC.

A good part of GOP officeholders’ fealty to Trump will be based on ongoing fear of stirring the anger of a mercurial man and his supporters, whose loyalty appears undiminished.

“Trump supporters are fervent about him, so there is a danger that if an elected official crosses Trump, they may incur the wrath of Trump — whether it’s in two years in an election or down the road,” said Peake.

The party’s chaos in Georgia has been an object lesson in the risks Republicans face if Trump believes they’ve crossed him.

He has repeatedly attacked Kemp after backing his 2018 gubernatorial bid; Kemp now may face a primary challenge for reelection.

Sterling dramatized at his news conference the toll Trump’s fraud claims have taken on election workers.

Sterling said he has police protection outside his home. Caravans of protesters had congregated outside Raffensperger’s house, and Raffensperger’s wife of 40 years had gotten sexualized threats over her cellphone, Sterling said, while a young election worker had been harassed with threats, including from someone who hung a noose and said that “he should be hung for treason.”

Sterling addressed Trump directly and told him what few Republicans have been willing to: that the election is over.

“Mr. President, it looks like you likely lost the state of Georgia,” he said. “If you want to run for reelection in four years, fine. Do it. But everything we’re seeing right now, there’s not a path.”