Former Maine Senate President Troy Jackson is all but certain to become the Democratic nominee for U.S. Senate after delegates aligned with him swept the majority of 500 slots up for grabs during this weekend’s county-level delegate selection across Maine’s 16 counties. With his top rivals dropping out and throwing their support behind him on Sunday, Jackson appears headed toward the nomination at next weekend’s state Democratic Party convention in Bangor, setting up what promises to be a bruising and costly general election battle against longtime Republican Sen. Susan Collins. The race is one of roughly a dozen nationwide that will determine whether Democrats can reclaim the Senate majority, with the GOP currently holding a 53-47 edge.

Jackson, 58, is a fifth-generation logger from Allagash, a tiny town at the northern tip of Maine along the Canadian border, and his political journey has been anything but conventional. He first entered politics nearly three decades ago by physically blocking Canadian loggers from crossing into the United States in protest of Maine workers being passed over for jobs. He ran for office as a Republican in 2000 before winning a seat in the Maine House two years later as an independent, then finally joined the Democratic Party in 2004. His social views have also shifted dramatically over the years — he received a perfect score from Maine Right to Life as recently as 2010 and voted against legalizing same-sex marriage in 2009, stances he attributes to his Catholic upbringing in rural Maine. Today he strongly supports abortion rights and same-sex marriage, saying his views evolved once he came to see reproductive access as a fundamental human right and healthcare issue.

Jackson was already a familiar face on the statewide ballot this cycle, having launched a gubernatorial campaign last year that earned him an endorsement from progressive champion Sen. Bernie Sanders of Vermont. He finished third in the ranked-choice Democratic primary for governor but remained closely aligned with Graham Platner, appearing alongside him and Sanders at rallies throughout the spring. The two exchanged endorsements late in the gubernatorial race when Platner was still cruising toward the Senate nomination, and Jackson has positioned himself as the natural heir to Platner’s populist and progressive movement even though he was among the first to call on Platner to exit the race following an explosive report containing a rape allegation from a woman Platner had dated.

On policy, Jackson mirrors much of what made Platner’s campaign resonate with working-class voters. He is campaigning on raising taxes on billionaires, implementing Medicare-for-all, abolishing Immigration and Customs Enforcement, and opposing military aid to Israel — positions that place him firmly on the party’s left flank even as some progressives note his more moderate past. Jackson has argued that the movement Platner built was never about one person and that he is best equipped to carry forward fights against the healthcare and pharmaceutical industries, strong unions, higher wages, and reproductive freedom. Whether that message can translate against a well-funded incumbent like Collins remains the central question heading into November.