Blue Hill, Maine - Graham Platner clinched victory in Maine's Democratic primary on Tuesday, seizing the nomination and setting up a one-on-one race against incumbent Senator Susan Collins.

Platner, a Marine veteran and oyster farmer, defeated Maine's Democratic Governor Janet Mills in Tuesday's primary, who remained on the ballot despite suspending her campaign, along with lesser-known candidate David Costello.

"I'm humbled and proud to officially be your Democratic nominee for the US Senate to take on Susan Collins and the billionaire class she represents," Platner posted to social media on Tuesday night.

"Susan Collins is spineless and corrupt. And in 147 days, we will defeat her," he wrote in a separate post.

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While around a quarter of votes still need to be counted, Platner has claimed 72% of Maine's Democratic primary vote as per current tallies, with Mills sitting at 19.6% and Costello at 8%.

The result isn't surprising, as Mills' decision to suspend her campaign effectively made Platner the presumptive nominee.

Platner's victory comes despite relentless pressure from the establishment wing of the Democratic Party, which backed Mills, and numerous scandals.

Just last week, Platner was accused of physical abuse and "unsettling behavior" by a Republican activist ex-girlfriend. The allegations came after a highly publicized sexting scandal mere days before.

Platner has acknowledged a troubled period in his life, saying he struggled with undiagnosed PTSD and alcohol abuse after his military service, but he denies physically harming any former partner.

Republicans are already preparing to make his past central to the general election. A Collins-aligned group is launching ads featuring Maine voters reading Platner's old online posts and calling him "too risky."

Platner stuck to his campaign message on Tuesday night while taking jabs at Collins.

"If you believe, as I do, that we can change our politics, and change our country, then you must also believe that people can change," Platner said during his victory speech in Blue Hill, his hometown.

"And the reason I believe that is because I have lived it – and the reason I have lived it is because of my wife," he continued.

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"To all those who feel let down, disappointed, or disillusioned, it is my job to earn your trust, your faith, and your support."

Platner then turned his attention to Collins, who he will face off against in the November midterm elections, targeting her record on abortion rights and support for President Donald Trump.

"Susan Collins does not serve us. She serves Donald Trump," Platner told the assembled crowd at his hometown's YMCA. "She serves the Epstein class."

"She serves her corporate donors and the corrupt political system that has rigged the economy against us. She does not serve us, and so we will defeat Susan Collins."