FILE- In a Nov. 3, 2008, file photo, voters wait to fill out absentee ballots the day before the general election in Detroit. People can cast absentee ballots in Michigan's March 10, 2020 presidential primary starting Saturday, Jan. 25, 2020. (AP Photo/Paul Sancya, File)

LANSING (AP) — Voting is underway in Michigan’s presidential primary more than a year after the option was greatly expanded through the passage of a ballot measure, though many Democrats vying for the nomination remain focused — for now — on Iowa and other early states.

The 45-day window to cast absentee ballots began Saturday. And unlike in the past, people can vote early for any reason.

It is expected to lead to what the secretary of state’s office called a “significant increase” in early voting, which already was on the rise before voters approved the 2018 constitutional amendment that allowed no-excuse absentee ballots.

Absentee ballots accounted for 18%, or 462,000, of the 2.5 million votes cast in Michigan’s 2016 primaries won by now-President Donald Trump and Vermont Sen. Bernie Sanders and more than a quarter, or 1.1 million, of the votes in the 2018 gubernatorial election. In local elections held on three days in 2019, the percentage of the overall vote share from absentee voting rose by between 4 and 15 points from 2017.

The advent of no-reason absentee voting means the dozen remaining Democratic candidates “need to be engaging with their coalition earlier,” said Patrick Schuh, state director for the liberal group America Votes. The outcome in the traditional first four voting states in February and the March 3 Super Tuesday primaries, he said, “will have potentially less impact on vote choice for voters here because they will have already voted.”

At this stage, though, Michigan’s primary has been mostly quiet since Democrats held debates in Detroit last summer, other than an ongoing barrage of TV ads aired by billionaire businessman Michael Bloomberg. He is skipping Iowa, New Hampshire, Nevada and South Carolina to focus on other states including Michigan, where his ad blitz has cost roughly $7 million, according to the Michigan Campaign Finance Network.

Bloomberg and Massachusetts Sen. Elizabeth Warren are the only two candidates with campaign offices in the state, both in Detroit. Warren was the first to hire a state director. Bloomberg was the last candidate to visit Michigan, on Dec. 21, and now has 60 staff on the ground.

A Bloomberg campaign official said it is sending mail and launching another voter-contact program focused on seniors, adding that it has been regularly calling senior voters and organizing senior-focused events. Other contenders include Sanders, former Vice President Joe Biden, Pete Buttigieg, the former mayor of South Bend, Indiana, and Sen. Amy Klobuchar of Minnesota.

A Buttigieg spokesperson said campaign volunteers are talking through the early-voting process with supporters. Sanders’ campaign said its volunteers have held nearly 700 events across the state.