TOMS RIVER, N.J. — The tables inside the hotel room were full and Andy Kim, the candidate responsible for filling them, was pleasantly surprised. It was a weeknight fund-raiser after all, rescheduled once already, for this relatively unknown Democratic challenger in a Republican district and a thick fog on Route 37 had obscured the tiny sign directing drivers to the hotel.

“Seven months before Election Day this is not normal, to be able to pack a room on a weekday,” he told a crowd of about 150 supporters, each of whom contributed at least $10 to listen to Mr. Kim and snack on donated croissants.

Ever since the election of President Trump, Democrats across the country have seen a predictable surge in energy among a base eager to take on the White House. What has been perhaps less expected is the uprising against the president coursing through more moderate suburbs, including many Mr. Trump won. Democrats buoyed by recent victories in Republican districts have lofty aims in suburban New Jersey as they work to wrest control of the House from the G.O.P., given Democrats’ surprise victories in Virginia, Alabama and, most recently, Pennsylvania.

In New Jersey, which has been described by Democrats and Republicans as the most suburban state in the country, the revolt has been especially muscular and has put into play Republican-held congressional seats that until this year had hardly been on the Democratic radar. Voters have grown increasingly angry with Mr. Trump, viewing many of his actions as damaging the state’s fortunes.