WASHINGTON, June 26 -- Bill Cassidy stood up in a room full of Republican senators and asked Donald Trump what was actually happening in Iran. The war was supposed to last four weeks. It had lasted four months. The objectives had not been met. What, Cassidy wanted to know, was going on?

Trump called him a lunatic.

Hours later, Cassidy voted to let Trump keep fighting the war without interference from Congress.

The sequence that played out Wednesday, June 24, compressed into roughly eight hours what has taken the Senate months to avoid resolving: whether any Republican is willing to sustain a check on a president conducting an unauthorized war. The answer, as of Wednesday night, was no.

The Senate had voted Tuesday, June 23, to pass a ...