SHELBY TOWNSHIP, Mich. — The shouting in the banquet hall erupted just minutes after the Macomb County Republican Party convention was called to order.

In a room packed with about 500 people, Mark Forton, the county party chairman and a fierce ally of former President Donald J. Trump, began railing against the establishment Republicans in the audience. A plan was afoot to oust him and his executive team, he said.

“They’re going to make an overthrow of the party, and you have a right to know what this county party has done in the last three years,” he said as his supporters booed and hollered and opponents pelted him with objections. Republicans in suits and cardigans on one side of the room shouted at die-hard Trump supporters in MAGA hats and Trump gear on the other.

The night ended as Mr. Forton had predicted, with a 158-123 vote that removed him and his leadership team from their posts.

The raucous scene in Macomb County exploded after months of infighting that roiled the Michigan Republican Party, pitting Trump loyalists like Mr. Forton, who continue to promote Mr. Trump’s lies about a stolen 2020 presidential election, against a cohort of Republicans who are eager to move on. The splintering threatens to upend the upcoming Republican state convention, where county precinct chairs vote on nominees for secretary of state, attorney general and other statewide offices.

Mr. Trump is all in on trying to sway those contests — and other races across the state, which he lost by 150,000 votes in 2020. The former president has endorsed 10 candidates for the State Legislature, including three who are challenging Republican incumbents, and has already picked his favorite candidate for speaker of the State House next year. Mr. Trump also has made numerous personal entreaties to shore up support for Matthew DePerno, who is running for attorney general, and Kristina Karamo, a candidate for secretary of state.

In Michigan and other battleground states, Mr. Trump’s chosen candidates have become megaphones for his election claims — frustrating some Republicans who view a preoccupation with the 2020 election as a losing message in 2022.

Republicans in Wisconsin and Arizona have encountered similar fractures over support for continued investigations into the 2020 election, and Mr. Trump’s attempts to play kingmaker in the Ohio Senate race is splintering Republicans there as well.

The root of the rupture in Michigan can, in part, be traced to endorsements made by Meshawn Maddock, a co-chair of the Michigan Republican Party and a Trump confidante. The Republican Party leadership has traditionally stayed out of statewide races, especially before the state convention. But Ms. Maddock endorsed Ms. Karamo and Mr. DePerno.

Both candidates have been vocal supporters of Mr. Trump’s falsehoods about the 2020 election. Mr. DePerno was one of the lawyers involved in Republican challenges in Antrim County, Mich., where a quickly corrected human error on election night spawned a barrage of conspiracy theories.Ms. Karamo belongs to a slate of “America First” secretary of state candidates running across the country and campaigning, in part, on distorted views of the 2020 election.

Beyond her endorsements, Ms. Maddock has been working to help prepare convention delegates. Last month, Ms. Maddock attended a mock convention held by the Michigan Conservative Coalition and reiterated glowing praise from Mr. Trump for Ms. Karamo, Mr. DePerno and John Gibbs, the conservative challenger to Representative Peter Meijer, a Republican congressman who voted to impeach Mr. Trump over the Jan. 6 Capitol riot.

“He was so fired up about Michigan,” Ms. Maddock said of conversations with Mr. Trump as she spoke during a question-and-answer session at the mock convention, according to audio of the event obtained by The New York Times. “This man cannot stop talking about Matt DePerno, Kristina Karamo, John Gibbs, who’s running against Peter Meijer.”

In a statement, Mr. DePerno said he’s “proud that local and state party leaders have endorsed my campaign. Ms. Karamo’s campaign did not respond to a request for comment.

Republican candidates facing Mr. DePerno and Ms. Karamo were taken aback by the endorsements and were outraged at the meddling by the state party leadership before the convention. Ms. Maddock, some candidates charged, appeared to be trying to tip the scales in favor of Trump-backed candidates.

Beau LeFave, a Republican state legislator who is running for secretary of state, said that he had spoken to both Ms. Maddock and her husband, State Representative Matt Maddock, “multiple times” before jumping into his race. They told him they were both rooting for him “and that they’re going to stay out of it,” he said.

“So it was quite a surprise to find out that they lied to me,” Mr. LeFave said.

Ms. Maddock was not available for an interview, according to Gustavo Portela, a spokesman for the Michigan Republican Party. He said that co-chairs had endorsed candidates in the past but acknowledged that the dynamic this cycle was a bit unusual.

“You’ve never had a co-chair who has been this close to a former president, who arguably has a lot of influence on the convention floor,” Mr. Portela said. He added that the party believes the contested races ahead of the convention were “a good thing” that “speaks to the frustration with the direction of our country, and more importantly, the direction of the state.”

The state party has struggled with other conflicts. After more than a year of hearing specious claims about vote counts and election equipment, some activists began questioning why the party would use tabulation machines. A group called Unity 4 MRP started an online campaign to pressure the party to count paper ballots by hand rather use the major brands of voting machines.

“Grassroots groups would sooner stare into the glowering, red eyes of Beelzebub than to allow a Dominion, ESS, or Hart tabulator to run its lecherous paws over their sacred ballots,” another group, Pure Integrity Michigan Elections, wrote in an email to supporters, according to The Detroit Free Press.

Eventually, the party leadership announced a concession: an audit of the convention vote overseen by a former secretary of state. But that didn’t please everyone.

“We have state committee members who fought hard to make sure that you do not have a hand count, and you need to ask why, and you need to be angry, and you need people figuring it out,” said J.D. Glaser, an activist who attended a rally of election skeptics in February. “This is our Republican Party. They’re working against you.”

The Macomb County Republican Party convention was one of 83 county meetings held Monday to pick the delegates to the statewide Michigan Republican Party endorsement convention on April 23.

In the weeks leading up to the event in the Detroit suburbs, Mr. Forton, a retired autoworker and longtime political activist, had rankled prominent Republican elected officials with his conspiracy-theory-laden assertions about the election and what he has described as “a cabal” of Democrats and Republicans who have been installed to control the country.

Presiding over the convention, Mr. Forton argued that his wing of Trump supporters had revived the county party, replenished its coffers and helped usher in a wave of Republican victories in the state. He slammed what he viewed as the old-guard Republicans in the room, some of whom were preparing the way to vote him out of office as he spoke.

“They have been wanting to take this county party back for a long time,” he said, adding that he and his supporters were “not going away.”

Some on Mr. Forton’s side of the room were attending a convention for the first time, spurred to do so, they said, out of concern for the direction of the party and outrage over the lack of audits and investigations into the results of the 2020 presidential election.

“What is happening here should be calm and exciting, but what you have is a Republican Party that does not think the same,” said Tamra Szacon, who earlier had led the prayer and was decked out in a cowboy hat and glittering American flag heels. “One of our biggest things is that we believe the election was stolen — a lot of people do.”

On the other side of the room, Republicans said they were frustrated with the bickering. Natasha Hargitay, a 35-year-old single mother, said she had been to more than a dozen conventions and had never been to one so contentious. She described herself as “Switzerland,” neutral in the fight. Still, she had not been pleased with Mr. Forton’s comments.

“I lost a lot of respect for him when he said, ‘We are the real Republicans,’” she said. “That means you are dividing the Republican Party.”

After the commotion, Eric Castiglia, who was elected the county’s new chairman, pledged to welcome all Republicans into the fold. He said he believed the state convention, with its machine and hand count election, would provide an opportunity to show election skeptics that the process could be fair.

“We have to start working on what we’re going to do with our values and not be a place where every candidate is a RINO, or not a Republican enough,” Mr. Castiglia said in an interview, using shorthand for “Republican in name only.”

But Mr. Forton has no intention of moving on. On Thursday, he filed a petition to state party leaders appealing his ouster.