Two supporters who were scheduled to campaign on the ground for him — Senator Rand Paul of Kentucky and Representative Matt Gaetz of Florida — hitched a ride home Monday night on Air Force One instead, to deal with legislative matters in Washington or attend the transfer of remains for two soldiers killed over the weekend in Afghanistan. Taking their place were prominent New Hampshire Republicans, a change from four years ago.

Gov. Chris Sununu bound into a local high school, where he purchased a box of Krispy Kreme doughnuts from a student bake sale and stayed on message.

“The Trump tax cuts here worked,” he said. “The U.S.M.C.A., very powerful, for a lot of our businesses that trade with our friends to the north. The regulatory reform streamlined the process.” He also credited the administration with investing $50 million in the state to battle the opioid crisis.

The last time Mr. Trump was running, John H. Sununu, the current governor’s father and a former governor himself, questioned Mr. Trump’s history of business losses and said his coarse language was “demeaning of the office he’s seeking.”

Trump campaign officials said they blamed the president’s 2016 loss in large part on his feud with Kelly Ayotte, a senator at the time who was locked in a close re-election race and tried to thread the needle by saying she would vote for Mr. Trump but not endorse him. Ms. Ayotte lost her seat, and Mr. Trump lost the state, an outcome one campaign official described as a political murder-suicide.

Monday found Ms. Ayotte campaigning for the president at a “Cops for Trump” event with Ivanka Trump and Vice President Mike Pence. Reached on the phone on Tuesday, Ms. Ayotte hung up on a reporter. “I’m busy. I have to go,” she said when asked to comment on the state of the race in New Hampshire.

But the show of Republican force appeared to be having its desired effect of sparking fears among Democratic voters about the strength of their own candidates.