For Trump, the consequences could be far more immediate.

A Democratic victory in this traditionally conservative and wealthy swath of suburbia would probably rattle Senate Republicans as they try to jump-start legislation to overhaul the nation’s health-care law by the end of this month. And it would raise questions about whether Trump has retained a strong hold on his party’s base as he turns to other policy ambitions this summer.

“I think this race is a wake-up call to the party and the political arm of the administration to pay attention to what they are doing and not doing that could potentially impact future success for the party at the ballot box,” said former Republican National Committee chairman Michael Steele.

Inside the West Wing, Trump and his advisers have paid increasing attention to the race and have been briefed regularly on Handel’s standing in private polls, GOP ground efforts and early-vote totals, according to a White House official. In particular, the official added, strategist Stephen K. Bannon and chief of staff Reince Priebus have been involved in discussions about the race and possible ramifications.