Troy Jackson, a Maine politician who began his career as a socially conservative Republican, has undergone a significant shift toward progressive positions over the course of his political life. Currently a Democrat and former president of the Maine Senate, Mr. Jackson is expected to secure his party’s nomination for the U.S. Senate this weekend following the withdrawal of his primary rivals. His evolving stance on social issues, particularly abortion and LGBTQ rights, as well as his longtime advocacy of economic populism, are drawing close scrutiny ahead of the general election.

Mr. Jackson’s early political career was marked by opposition to abortion rights and same-sex marriage. In the early 2000s, he earned perfect scores from Maine Right to Life, an anti-abortion group, and supported legislation that would have recognized fetuses as persons with legal standing in certain cases. He also voted for measures such as a 24-hour waiting period for women seeking an abortion. Raised Catholic, Mr. Jackson has described himself as “conflicted” on abortion during that period, citing a difficult personal journey in coming to terms with the issue.

By 2017, as he rose within Democratic leadership, Mr. Jackson shifted his views, aligning with his caucus in support of abortion rights. In 2023, he played a role in passing a Maine law that permits abortion at any stage of pregnancy as long as a doctor deems it necessary. He has since received high ratings from Planned Parenthood and LGBTQ advocacy groups, reflecting a departure from his previous positions. Mr. Jackson has acknowledged past mistakes, stating that he is “really, really proud” of changing his stance and doing “the right thing.”

Economic populism has been a consistent theme throughout Mr. Jackson’s career. Beginning with organizing workers against cross-border job outsourcing in the late 1990s, he later ran for political office initially as a Republican, then an independent, and finally a Democrat. His 2014 congressional campaign emphasized opposition to free trade deals and corporate influence, defending calls for a single-payer healthcare system and criticizing income inequality and political corruption. Though unsuccessful in that bid, his platform echoed themes prominent in progressive circles.

Mr. Jackson’s temperament and personal conduct have also become topics of interest. Colleagues have recounted an incident four years ago during a heated discussion over prescription drug costs when Mr. Jackson threw a half-full water bottle in frustration. Witnesses emphasized that it was not directed at anyone and that Mr. Jackson subsequently apologized. Some viewed the episode as indicative of his passionate style, while others found it concerning. Mr. Jackson acknowledged the outburst but declined to apologize for his passion.

If nominated, Mr. Jackson will face incumbent Senator Susan Collins, a five-term Republican known for her moderate positions. Both parties regard the Maine Senate race as critical to the national balance of power. Democrats have sought to highlight Collins’s 2018 vote to confirm Supreme Court Justice Brett M. Kavanaugh, who contributed to overturning Roe v. Wade, though Mr. Jackson’s earlier anti-abortion record may complicate that critique. Mr. Jackson has focused his campaign messaging more on economic issues than social ones, portraying himself as a principled advocate willing to fight for Maine’s working class.

As the nomination process concludes and the general election approaches, observers will continue to evaluate how Mr. Jackson’s political evolution and personal history shape his appeal to voters in this pivotal contest.