The country’s next high-profile special election is in August for an open House seat near Columbus, Ohio. Once a solidly Republican seat in a district Mr. Trump carried easily, the race is now a tossup, according to nonpartisan analysts, thanks to an energized Democratic base. The candidates were finalized on Tuesday: Danny O’Connor, a Democratic official in Franklin County, will oppose Troy Balderson, a Republican state senator.
In the United States Senate race, Ohio Republicans chose Representative James B. Renacci to try to unseat Senator Sherrod Brown, whose old-school progressivism — opposing trade deals, championing labor — aligns with part of Mr. Trump’s blue-collar appeal.
“My message is consistent and will continue to be — I’m going to fight for the little guy regardless of whether she works in an office or works in a diner,” Mr. Brown said in a telephone interview. He suggested he would not make a point of going after Mr. Trump.
“I will do what I do,” he said. “I don’t have this grand strategy. I think if you do this job the way you should, elections largely take care of themselves.”
In Indiana, Senator Joe Donnelly, one of the most vulnerable Democrats, noted that he had voted with Mr. Trump 62 percent of the time in the Senate and had backed 70 percent of the president’s nominees.
“If President Trump is right on an issue, I will be with him every time,” Mr. Donnelly said in a conference call with reporters Tuesday night. “When he’s not, I will pass. My job is not to be a cheerleader for the president, my job is not to be a cheerleader for a party leader or a party.”
Mr. Donnelly is matched against Mike Braun, a wealthy businessman who ran as a political outsider, and who Republicans believe will serve as validation of Mr. Trump’s policies and anti-Washington appeal.