Mr. Kean, a former state senator and assemblyman, has said he supported a “woman’s right to choose.” But he opposes abortion after 20 weeks of pregnancy absent extenuating circumstances, according to his campaign.

“I think there are meaningful exceptions that should be rape, incest, life and the health of the mother,” he said Sunday. “Those are exceptions for a reasonable amount of time.”

In the Senate, he voted against a bill affirming abortion as a right in New Jersey. He said he opposed the legislation, which was later signed into law, because it permitted abortion at any point in a pregnancy, including what he called late-term abortion. Abortions after 21 weeks of pregnancy are rare, accounting for less than 1 percent of all abortions performed in the United States in 2019, according to the Centers for Disease Control and Prevention.

A Kean campaign website is less nuanced.

“Tom is a fierce defender of the sanctity of life, fighting every step of the way to protect the unborn from egregious abortion laws proposed in New Jersey, and will continue to do so in Congress,” it reads.

“When I’m talking about the egregious piece of legislation, the ability to choose to terminate, for not valid reasons, when a baby can stay alive, be alive, outside of the womb, is wrong,” he said at the forum.

Of the 616,000 registered voters in the district, about a third are not enrolled in either major party. It is these moderate voters who tend to sway elections in New Jersey.

Motivating supporters to turn in mail ballots or to show up at polling places during an election year with no statewide races is crucial for any candidate, said Debbie Walsh, director of the Center for American Women and Politics at Rutgers.