Senator Cory Booker’s staff members described a nagging fear as they worked for a week to fill 15 binders with enough material to cover what would soon become a history-making, 25-hour speech.

What if no one listened?

Their worry was short-lived. By 11 a.m. on Tuesday, 16 hours after Mr. Booker, Democrat of New Jersey, had begun railing against President Trump’s policies on the floor of the U.S. Senate, roughly 14,000 callers had left messages on his office hotline, aides said. Before he finally stopped speaking, the office had fielded 14,000 more.

For 25 hours and five minutes, Mr. Booker, who will turn 56 this month, did not sit or exit the Senate chambers to eat or use a bathroom. His speech broke, by nearly an hour, a record set 68 years ago by Senator Strom Thurmond of South Carolina, a segregationist who at the time was trying to block civil rights legislation.

Americans noticed. The social-media-savvy senator streamed the speech live on his TikTok account, where it garnered more than 350 million “likes.” And more than 110,000 people were watching on YouTube when Mr. Booker ended his soliloquy in much the same way he began: with a homage to a mentor, the civil rights pioneer John Lewis, a Georgia Democrat who spent three decades in Congress. “Let’s get in good trouble,” he said, borrowing Mr. Lewis’s famous call to action.

Many of those watching appeared to revel in Mr. Booker’s stamina and moxie.

“New respect for New Jersey,” a YouTube viewer wrote in a live chat message two hours before the senator stopped talking.

Democrats have been mainly relegated to the sidelines since Mr. Trump was inaugurated in January and began signing a barrage of executive orders meant to reshape government, rushing to try to shut down federal agencies, fire federal employees, defang law firms he opposes and deport international students who have spoken out against Israel’s war in Gaza.