BANGOR, Maine– Maine Democrats will choose a new U.S. Senate candidate on Saturday to take on veteran Republican Sen. Susan Collins in a race that could decide control of the Senate, after Graham Platner dropped out of the race following a sexual assault allegation.

Support has centered around former state Senate President Troy Jackson, a fifth-generation logger from rural northern Maine who campaigned alongside Platner during a failed gubernatorial bid and was a favorite among progressives to replace him.

The Maine Democratic Party has been struggling to elect a new candidate after Platner, who cruised to victory in the Democratic primary in June, was accused by an ex-girlfriend of sexually assaulting her in 2021. Platner denies the allegation, but dropped out of the race after key supporters asked him to drop out.

Democrats have viewed Maine as the party’s best chance to flip a Senate seat this year because it is a competitive Senate race in a state President Donald Trump lost in 2024. But defeating Collins won’t be easy. The five-term incumbent has a fundraising advantage, while the new candidate will have less than four months to sell himself to voters.

Maine law gave the state party authority to choose a replacement and required a new candidate to be named by Monday, 99 days before the Nov. 3 election.

The never-before-used voting process by Maine Democrats to choose a new candidate will involve more than 600 Democratic delegates meeting in Bangor, about 130 miles (209.21 kilometers) north of Portland. Delegates were elected at county party meetings last weekend.

“We have worked hard to create a fair process that includes diverse viewpoints and diverse backgrounds from Democrats across the state of Maine, as we all come together in service of our ultimate goal: defeating Susan Collins and winning this Senate seat,” the party said in a statement.

Once Platner dropped out on July 10, a flood of former gubernatorial candidates, including Jackson, and others jumped in to try to take Platner’s place. But by July 19, most had abandoned their bids, and Jackson emerged as the clear favorite.

Jackson received initial support from progressives who had backed Platner before he dropped out. Our Revolution, the political organization founded nearly a decade ago by Sen. Bernie Sanders, initially endorsed Jackson for governor and Platner for Senate. When Platner dropped out of the race, the group rallied behind Jackson.

Jackson previously ran Maine operations for Sanders’ presidential bid in 2016. This election cycle, Sanders endorsed Jackson for governor and Platner for Senate, although the independent senator from Vermont withdrew his support for Platner after the sexual assault allegation. He said he did not plan to weigh in on which Democrat should replace Platner.

Only one other candidate has remained in the race for the Senate nomination: women’s health company CEO Saundra Pelletier. He faces long odds against Jackson, who has been a fixture in Maine politics for more than a decade.

Jackson’s campaign says more than 480 of the 601 delegates who will vote at Saturday’s convention are committed to supporting him.

Jackson has supported progressive positions such as Medicare for All. He has also called for the abolition of Immigration and Customs Enforcement, whose presence in Maine has been the subject of heated debate since an agent killed a driver in the state earlier this month.

Democrats have a narrow path to taking back the Senate in November and are highly unlikely to be able to do so without a victory in Maine. Plus, they need wins in competitive races in North Carolina, Alaska and Ohio, and they need to keep the seats they already have. That includes open Senate seats in Michigan and Minnesota, where Democratic incumbents are retiring.

Maine’s Democratic primary was one of the first contests in which progressives faced off against establishment-backed Democrats. While Platner faced several controversies during her campaign, she easily bested Gov. Janet Mills, who was endorsed by Senate Democratic leader Chuck Schumer, but dropped out before the June 9 primary.

Platner was endorsed by Sanders, as well as Arizona Sen. Rubén Gallego and Massachusetts Sen. Elizabeth Warren. That support disintegrated after the sexual assault allegation earlier this month.

If he becomes the nominee, Jackson will have to convince the state’s large bloc of independent voters that it is time to replace Collins. Republicans have called Jackson too extreme for Maine voters, and Collins said earlier this week that he knows Jackson well and that his positions are “clearly” in line with socialism.

He noted that Jackson ran Sanders’ first presidential campaign in Maine, adding that “he’s a Bernie brother.”

Jackson would also need to fight to make up a fundraising gap against Collins, who has been raising money for months.

Federal documents show it has raised more than $16 million so far. Jackson’s campaign said this week that it has raised more than $1 million since entering the Senate race.

Jackson believes his team is up to the task.

“We are building a movement in every corner of this state to defeat Susan Collins and elect a senator who will fight like hell for working people,” Jackson said last week.

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AP writer Nathan Ellgren in Washington contributed to this report.