With a strong governor, a Legislature passing a raft of liberal measures and a looming early presidential primary, Democrats are testing the promise and pitfalls of complete control of the state.The governor of Michigan is considered one of her party’s brightest stars. Her state’s Democratic-controlled Legislature is rapidly approving a raft of ambitious priorities. The Democratic Party is planning to host one of its earliest presidential primaries in Michigan, while the state’s Republican Party is in chaos.Seven years after Michigan helped cement Donald J. Trump’s presidential victory, the state has transformed into a new — if fragile — focal point of Democratic power, testing the promise and pitfalls of complete Democratic governance in one of the nation’s pre-eminent political battlegrounds.Michigan’s Democratic leaders, however, recoil at the idea that their state — once a reliable stronghold for the party in presidential years — is turning blue once more.“No! Michigan’s not a blue state,” Gov. Gretchen Whitmer insisted in an interview last week in Bay City, nestled in a windy, working-class county near Saginaw Bay that Mr. Trump won twice. Ms. Whitmer captured it too, prevailing there and across the state in Democrats’ November sweep.“It would be a mistake for anyone to look at that and think Michigan is not still a tossup, very competitive, very diverse state that’s going to decide the outcome of the next national election again,” she said.“Everybody thinks, Oh, Michigan’s done, it’s a blue state,” added Representative Debbie Dingell, a Michigan Democrat. “Tenuous is the operative word.”Against that backdrop — significant victories last fall, in a state that is still closely divided — state Democrats are pursuing a flood of liberal legislation, while measuring the durability of an unwieldy coalition that defeated Republicans in the last three elections.Democratic triumphs were fueled by both moderate suburbanites and liberal city dwellers, left-wing college students and even some onetime Trump voters who thought their party had gone too far.“The state Republican Party is not reflective of the average Republican in Michigan,” Ms. Whitmer said, nodding to the hard-right turn of the Michigan G.O.P. “I don’t think that everyone’s all of a sudden become Democrats.”In November, Michigan voters decided to enshrine abortion protections in the State Constitution. Brittany Greeson for The New York TimesMs. Whitmer has cautioned against claiming political “mandates.”But Democrats have moved assertively to act on their power, which includes full control of the Legislature and governor’s mansion for the first time in 40 years, focusing on both pocketbook priorities and cultural issues.They have shepherded through a major tax package, and, to the consternation of some in the business community, made Michigan the first state in nearly 60 years to repeal right-to-work rules, which had weakened organized labor. They have expanded L.G.B.T.Q. protections and pursued anti-gun violence measures, and have moved to repeal a now-unenforceable abortion ban from 1931.Ms. Whitmer has also signed a measure moving up Michigan’s presidential primary, a move blessed by national Democrats, though it is unclear how Republicans will proceed.If that calendar change takes hold, voters around the country who were once made intimately familiar with the Iowa State Fair may soon become acquainted with the Posen Potato Festival and a Michigan cheeseburger festival, as the state moves into a position of greater prominence in the Democratic nominating process.Ms. Whitmer’s victory margin of nearly 11 percentage points — on par or ahead of governors in several more liberal states — has only encouraged a perception among many Democrats that she is possible presidential material.But she insisted she would not run for president in 2024, regardless of President Biden’s re-election plans. He is expected to run and would have strong support from party leaders including Ms. Whitmer, but has not yet announced a bid.Ms. Whitmer holding a discussion with students and faculty members at a career center in Bay City, Mich., this month. Many Democrats see her as a potential presidential candidate one day, but she has insisted she will not run in 2024.Emily Elconin for The New York Times“I have made a commitment to the people of Michigan, I’m going to do this job till the end of this term,” Ms. Whitmer said. Pressed on whether there was anything about the presidency that appealed down the road, she first demurred — “no, not at the moment” — before allowing, “I think that this country is long overdue for a strong female chief executive.”Republicans, for their part, who as recently as 2018 controlled the state levers of power, are now adrift and divided. Ahead of what should be a marquee Senate race to succeed Senator Debbie Stabenow, a Democrat who is retiring, the challenge of nominating someone who would both survive a primary contest and thrive in a general election is growing more apparent by the week.The state Republican Party is now helmed by an election denier, Kristina Karamo, who lost her November race for secretary of state by 14 points and has stoked doubts about her ability to run a serious operation.“People have concerns that the incumbent will have trouble raising money when she openly maligns the same donors she needs to bring in to help win the Senate race,” said Gustavo Portela, a former spokesman for the Michigan Republican Party. “She’ll have a challenge being able to balance the grass roots and donors.”Former President Donald J. Trump endorsing Kristina Karamo, left, who would go on to lose Michigan’s race for secretary of state in November. She is now the leader of the state Republican Party. Brittany Greeson for The New York TimesMs. Karamo did not respond to requests for comment.Just last week, the Michigan G.O.P. promoted an image on social media that compared efforts to curb gun violence with the Nazis’ theft of wedding rings from Holocaust victims, then defended the posts amid a backlash.“The Republican Party in Michigan is dead for the foreseeable future,” said former Representative Dave Trott, who represented a suburban Detroit district as a Republican but now considers himself an independent, supporting Mr. Biden in 2020. “Even if the right people were in charge, the MAGA movement is such that any candidate that would be more acceptable to a general electorate can’t win the primary.”“If I’m Elissa Slotkin,” he added, “I’m already trying to figure out which Senate building I want my office in.”The primary and the general elections for Senate are political lifetimes away, but Ms. Slotkin, a Democratic congresswoman from a competitive district, is currently in a commanding position in the race.Several of the state’s highest-profile Democrats have passed on a Senate run, giving her running room in the primary, though a number of other Democrats — hoping to see more representation of Black voters, Detroit voters, or both in the race — could still get in. Among Republicans, former Representative Peter Meijer, who voted to impeach Mr. Trump, is perhaps the best-known potential candidate. Kevin Rinke, who ran a largely self-funded Republican primary campaign for governor, has also been seen as a possible contender, among others. Both men lost primaries last year to far-right candidates who were then defeated in general elections.Representative Elissa Slotkin, a Democrat, joined Michigan State students at the State Capitol who were protesting gun violence two days after a deadly shooting on the university’s campus. Nick Hagen for The New York TimesMaggie Abboud, a spokeswoman for the National Republican Senatorial Committee, said the committee had seen “a number of strong potential candidates reach out.”Certainly, it is difficult to predict how the Democratic strength on display last fall will translate in 2024. The contests were defined in part by an extraordinary backlash to the overturning of Roe v. Wade and a major, successful initiative to enshrine abortion protections in the State Constitution — and it is far too early to say what issues will be galvanizing next year.Democrats benefited from a redistricting process. And party leaders freely acknowledge how quickly the political environment in the state can shift.“We were looking into the brink and decided to work our backsides off,” Ms. Slotkin said. “The minute you sleep on Michigan, it can go the other direction.”There were also warning signs in Wayne County, which is home to Detroit and the state’s largest population of Black Americans. Turnout was lower in 2022 than it was in the 2018 midterms.“We have an opportunity to do more,” said Lt. Gov. Garlin Gilchrist II, himself a Detroiter. “I certainly spent a lot of time with Black voters and particularly our younger voters and our Black male voters who we’ve got to make sure are deeply engaged, and that we invest in that engagement.”Still, the party’s gains were significant, including signs of new inroads in white working-class territory that has become exceedingly difficult for Democrats around the country.“In my district, folks were outraged by Jan. 6, but if that’s all you talk to them about, you’re not going to win their vote,” said State Senator Kristen McDonald Rivet, a Democrat whose seat includes parts of Bay County, and who emphasized both kitchen-table economic issues and abortion rights in her race.Kristen McDonald Rivet, a Democratic state senator, said her party was mobilized “in a way that I haven’t seen in a really long time.”Emily Elconin for The New York Times“By demonstrating that we are moving on real issues that people care about and doing it very aggressively with Democratic power,” she said, she hoped Michiganders would believe that “voting for a Democrat means things are going to get better.”Democrats “were really demoralized after the Trump victory, and suddenly we are seeing people coming to party meetings again,” she added. “The Democratic trifecta in Michigan has mobilized Democrats in a way that I haven’t seen in a really long time.”But Ms. Dingell, the Democratic congresswoman, remains keenly focused on pro-Trump sentiment in the state, and she is already warning of another challenging election cycle, arguing that races up and down the ballot will be highly competitive.“We will be ground zero for every race,” she said. 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