Susan Collins

Of the more than 10,000 votes cast by Senator Susan Collins of Maine, there is one that has shadowed her like no other as she runs for a sixth term.

On Oct. 6, 2018, Ms. Collins, one of only two Senate Republicans who support abortion rights, cast a deciding vote to confirm Brett M. Kavanaugh to the U.S. Supreme Court. Four years later, Justice Kavanaugh voted with the conservative majority to overturn Roe v. Wade, which had guaranteed a constitutional right to abortion for nearly half a century.

The vote cut against her well-cultivated reputation as a moderate Republican who is unafraid to break ranks. It also put her at odds with abortion rights activists, who had previously backed her campaigns, and with advocates for victims of sexual violence, who rallied behind a woman who accused Mr. Kavanaugh of sexual assault, an allegation he denied.

Now, Ms. Collins’s support for Justice Kavanaugh has become a major issue in her first re-election campaign since Roe was overturned, a race that could swing control of the Senate. The 2018 vote has emerged as a character test of Ms. Collins for Maine voters: Some consider her a principled lawmaker taking tough votes, while others see a calculating politician determined to keep her job.