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…