Empowered by an Odds-Defying Win, Susan Collins is Ready to Deal

“My winning shows that a moderate can prevail in this highly polarized environment,” Ms. Collins said. “My victory in Maine shows that you can be an independent voice and take some breaths, do what you think is right, and the voters, in some states at least, will reward you.”

Ms. Collins said she was open to working with former political foes in order to achieve legislative accomplishments. But having survived a brutal campaign in which Democrats savaged her, Ms. Collins has reason to hold some grudges. She pointedly noted that Senator Chuck Schumer, Democrat of New York and the minority leader, presented “a challenge” given “the millions of dollars in blatantly false ads he ran against me.”

Though the precise balance of the power in the Senate will remain unknown until two Georgia runoff races are decided in early January, Republicans are favored to win both seats, likely leaving Mr. Biden as the first Democratic president since Grover Cleveland in 1885 to take office without Democrats in control of both congressional chambers. A fraction of Republican support — likely, that of Ms. Collins and Senator Lisa Murkowski of Alaska, who faces re-election in 2022 — will be needed to advance both his legislative and political ambitions.

“It puts her in a very strong position to get things done in the Senate,” said Steve Abbott, her campaign manager and a longtime adviser. He described “a special self-confidence that comes” from “beating the odds,” one that, he added, “strengthens her to the core, to do what she thinks is right.”

In a signal of where the power could rest in the 117th Congress, Mr. Biden has yet to speak to Senator Mitch McConnell of Kentucky, the Republican leader. But he made a point of calling Ms. Collins before his own victory was cemented. (Mr. Biden formally endorsed Ms. Gideon during the campaign, but did not appear in person with her.)

“I know we come technically from political backgrounds that are different, but they’re not that different,” Mr. Biden said in a 2017 video filmed in honor of Ms. Collins receiving an Irish Heritage Center award. “We’ve become fast and good friends, and I look forward to you continuing to lead in the United States Senate, Susan.”