James Craig, a former Detroit police chief, announced on Tuesday that he was running for the Senate seat in Michigan being vacated by Debbie Stabenow, a Democrat who is retiring after more than two decades in the position.
In an interview, Mr. Craig, 67, described himself as a conservative populist who would look to work with Democrats and Republicans on immigration, national security and law-and-order issues.
“This race will be decided by the voters, and they’re sick and tired of partisan politics and being lied to,” he said. “They want someone to look them in the eye and tell them the truth.”
Mr. Craig ran for governor of Michigan last year and was leading early Republican primary polls until he was disqualified because of forged signatures on his nominating petition.
But he enters the Senate race as an underdog. In the Republican primary, national party leaders are already backing former Representative Mike Rogers.
In the general election, Michigan is viewed by both parties as, at best, a secondary battleground because of consistent gains from Michigan Democrats in the three election cycles since Donald J. Trump’s victory there in 2016.
Mr. Craig said he was likely to promote his background in law enforcement as he campaigns on some of the conservative priorities that have helped propel Mr. Trump.
Mr. Craig said he had spoken to Trump campaign officials about his bid, but not to the former president. Mr. Craig said that he believed there were “legit issues raised” about election fraud in 2020, but that he did not think the election had been stolen from Mr. Trump.
“I know he’s been charged with a number of crimes, but he hasn’t been found guilty,” Mr. Craig said of the former president’s indictments. Asked whether Mr. Trump was the nominee for the party because of his large polling lead, he said, “At this point, I have to say he is.”
National Republicans have privately expressed concerns about Mr. Craig’s candidacy, worrying that personal issues, including at least one bankruptcy and multiple divorces, could prove detrimental to his campaign.
Mr. Craig said he wouldn’t shy away from addressing questions about his past, noting that he had “decent relationships” with his ex-wives and “good relationships with my two adult children.”
“If someone asks me about it, I have no aversion to talk about it,” he said.
The campaign arm for Senate Republicans, the National Republican Senatorial Campaign Committee, has recruited Mr. Rogers, 60, to run for the seat. He began his campaign last month.
On the campaign trail, Mr. Rogers has tried to straddle the line dividing the party between its conservative grass-roots and pro-business moderates.
In the state’s Upper Peninsula recently, he vowed to help lower the cost of propane and other energy. On social media, Mr. Rogers — a former F.B.I. agent and House Intelligence Committee chairman — accused the Justice Department of “waging war” on Mr. Trump “on behalf of President Biden.”
The Democratic Party’s best-known candidate so far is Representative Elissa Slotkin, who was elected to Congress in the blue wave of 2018 and has won re-election twice in a swing district.
She had $3.7 million for the race as of June 30, according to the most recently available campaign finance report, well ahead of her primary opponents, who include Hill Harper, an actor; Nasser Beydoun, a businessman; and Pamela Pugh, the president of the State Board of Education.