Republicans Grapple With Next Moves if Democrats Replace Biden

As Sam Brown, a Republican and Army veteran, has campaigned for Nevada’s U.S. Senate seat against Senator Jacky Rosen, he has deployed a potent weapon against his Democratic foe: the unpopularity of President Biden among the state’s voters.

Mr. Brown and his campaign have linked Ms. Rosen to Mr. Biden and his policies at every turn, slamming her support for him on the campaign trail and online and even occasionally referring to her as “Jacky Biden.”

Now, with Mr. Biden’s future at the top of the Democratic ticket in doubt, Republicans like Mr. Brown, campaigning in competitive down-ballot races that could decide control of Congress, are considering whether they will need to alter their messaging to account for a different Democratic presidential nominee — whether that is Vice President Kamala Harris or another challenger.

“It certainly changes things; changing a potential presidential candidate for November, that’s going to do something,” Mr. Brown said in an interview. “But at the end of the day, Jacky Rosen has her own record that she has to answer to.”

Republicans viewed Mr. Biden as an easy target even before the renewed questions over his age and mental acuity stemming from his disastrous June debate performance. Many voters already viewed him as too old for a second term, and Republicans bashed him for his handling of the border and tried tying him to soaring inflation and gas prices.