Senator Mitt Romney, Republican of Utah, explained, “This is a vote for the Constitution and for the balance of powers that is at its core.”

Shortly after the vote Thursday afternoon, Mr. Trump took to Twitter. “VETO!” he wrote.

For the record, the Republican senators voting for the resolution (and against the president’s power grab) were, in addition to Mr. Romney: Lamar Alexander of Tennessee, Roy Blunt of Missouri, Susan Collins of Maine, Mike Lee of Utah, Jerry Moran of Kansas, Lisa Murkowski of Alaska, Rand Paul of Kentucky, Rob Portman of Ohio, Marco Rubio of Florida, Pat Toomey of Pennsylvania and Roger Wicker of Mississippi.

It is notable that this brushback of the president came just one day after the Senate voted 54 to 46 to end American support for Saudi Arabia’s brutal, four-year-old military venture in Yemen. Seven Republicans crossed party lines to pass a bill designed to claw back Congress’s responsibility for declaring war. The measure is expected to pass the House as well, provoking a second presidential veto.

In both cases, Mr. Trump lobbied Republicans, publicly and privately, to stand by him — if only to limit his margins of loss. He reportedly dangled funding promises in front of some members, even as he continued his Twitter taunts, including this Thursday gem: “A vote for today’s resolution by Republican Senators is a vote for Nancy Pelosi, Crime, and the Open Border Democrats!”

But neither sticks nor carrots were enough to spare the president back-to-back humiliations.

Senate Republicans were not exactly eager to cross Mr. Trump. In the lead-up to Thursday’s vote, members scrambled to avoid a confrontation. Mr. Lee put together a proposal to reform the National Emergencies Act. His bill, introduced Tuesday, would have automatically ended future declarations after 30 days, unless Congress voted to extend them. As an opening bid, the idea was worth debating, seeing as how the current law is clearly prone to abuse.