Maine Democrats chose Troy Jackson, a progressive former state legislator, to replace Graham Platner as their Senate candidate at a convention on Saturday that followed weeks of internal turmoil in a key battleground state.
Mr. Jackson’s victory, a vote of 566 to 5, came on the first ballot of a pop-up state convention the Maine Democratic Party organized in the 17 days since Mr. Platner, who faced a rape accusation he denies, dropped out of the race.
The coronation of Mr. Jackson, who has spent a quarter-century in Maine state politics, completes a tumultuous process since Mr. Platner was forced from the race. Mr. Jackson will face Senator Susan Collins, a five-term Republican who has stymied generations of Maine Democrats.
“Today we turn the page,” Mr. Jackson told delegates in Bangor, Maine. “Today, we begin the work of defeating Susan Collins in November.”
Mr. Jackson, 58, carries much of the progressive politics that powered the movement that lifted Mr. Platner from political obscurity. A former logger who entered politics in the late 1990s organizing against Canadian workers crossing the border to work for lower wages than Americans, Mr. Jackson now faces perhaps the biggest challenge of his political career.
He is up against Ms. Collins, a moderate Republican seeking a sixth term in office. The race, seen as a central battleground in the fight for control of the Senate, features two longtime politicians who grew up in the same county in northern Maine.
In the days since he has become the presumptive Democratic nominee, Mr. Jackson has sought to tie Ms. Collins directly to President Trump, who has lost the state in each of his three campaigns.
In his victory remarks Saturday, Mr. Jackson said Ms. Collins “has served Donald Trump” and condemned her votes to confirm his Supreme Court appointees and to fund the Trump administration’s immigration enforcement.
Ms. Collins — who has long portrayed herself as a moderate above the fray of the mudslinging of politics elsewhere — and her Republican allies have in turn sought to disqualify Mr. Jackson on personal grounds.
She recently dismissed Mr. Jackson as a “Bernie Bro” while the Maine Republican Party compared Mr. Jackson to Mr. Platner. The Senate Leadership Fund, the main super PAC for Senate Republicans, released a new advertisement attacking Mr. Jackson over reports he could be ill-tempered, saying he was “like Graham Platner, but worse.”
Ms. Collins, who appeared at a parade in Casco, Maine, on Saturday, said in a brief interview beforehand that Mr. Jackson had been “hyperpartisan in his approach” in state politics. “That contrasts with the bipartisan approach that I’ve taken in Washington,” she said.
A former president of the Maine State Senate, Mr. Jackson was one of a dozen Democrats who entered the abbreviated contest to replace Mr. Platner earlier this month. Like Mr. Jackson, many of them had waged losing campaigns for other offices earlier this year.
Following a condensed primary that included a single televised debate and a scramble to organize supporters, Mr. Jackson’s supporters won delegate elections by overwhelming margins at county party gatherings last weekend.
His main Democratic rivals subsequently dropped out, turning what could have been a messy convention into a clear victory for Mr. Jackson.
Maine Democrats are expected to formally submit his nomination to Shenna Bellows, Maine’s secretary of state, when her office opens on Monday. Ms. Bellows was one of the Democrats who sought to replace Mr. Platner and ended her campaign after Mr. Jackson’s show of force at the county meetings.
A fixture of Maine politics who speaks in the Aroostook accent of his state’s north woods, Mr. Jackson will now be thrust to the center of a Senate race that for the past year has attracted national attention and tens of millions of dollars.
While he is well known in Augusta and in state politics, Mr. Jackson has a low profile outside Maine or with national donors who fund the nation’s most competitive Senate races. He has not been viewed as a prolific fund-raiser in state politics.
A progressive economic populist who has rallied against big corporations and champions a “Medicare for all” universal health care system, Mr. Jackson began his political career quite conservative on social issues. For years he opposed abortion rights, voted against same-sex marriage and received high ratings from the National Rifle Association.
But Mr. Jackson adopted standard progressive positions as he rose in Maine politics. As the State Senate president, Mr. Jackson ushered through one of the nation’s most permissive abortion laws, allowing the procedure at any point in a woman’s pregnancy with a physician’s consent.
Some of Mr. Jackson’s colleagues from his time as the leader of the State Senate, which lasted from 2018 to 2024, recalled that at times he could be quick to anger.
Mr. Jackson’s left-leaning politics largely mirror those of Mr. Platner, who energized Maine Democrats through a series of town hall gatherings over the past year. The two campaigned together earlier this year as Mr. Jackson ran for governor, emphasizing a similar progressive mantle built around ideas such as abolishing Immigration and Customs Enforcement.
Mr. Platner, an oyster farmer who had never run for office before, faced a series of revelations about his past, including offensive online posts, a tattoo on his chest that resembled a Nazi symbol and allegations about his treatment of women.
Mr. Jackson is a veteran politician who has long been an adherent of Senator Bernie Sanders of Vermont, an independent who leads an impassioned left-wing movement. Mr. Jackson worked for Mr. Sanders’s 2016 presidential campaign and had the senator’s endorsement during his run for governor this year. In an interview on Monday, Mr. Jackson said Mr. Sanders, who caucuses with the Democrats, would be his first choice to be the leader of Senate Democrats next year.
Mr. Jackson said in that interview that he would not support Senator Chuck Schumer of New York, the minority leader, to remain in his post. Mr. Jackson also expressed reservations about receiving financial or other assistance from Mr. Schumer, whose allies oversee the super PAC devoted to electing Senate Democrats.
Esmé E. Deprez contributed reporting from Casco, Maine.
