As More Members Leave, House G.O.P. Will Be Able to Spare Just 1 Vote

Republicans in Congress continue sprinting for the exits.

Representative Mike Gallagher, Republican of Wisconsin, announced on Friday afternoon that he would resign from Congress months earlier than expected on April 19, bringing the already minuscule Republican majority down to a lonely one vote.

After his departure next month, Republicans will control 217 House seats to the Democrats’ 213, allowing the G.O.P. to afford only a single defection from the party line on votes when all members are present.

Mr. Gallagher, the four-term lawmaker who serves as chairman of the Select Committee on the Chinese Communist Party, provided no reason for his early exit in the brief statement he made announcing his plans. He said simply that “after conversations with my family, I have made the decision to resign my position,” and that he had “worked closely with House Republican leadership on this timeline.”

But leaders had not anticipated it. It came on a day that highlighted Republican disarray and division, as Speaker Mike Johnson pushed through a $1.2 trillion spending bill that prompted a revolt on his right flank and at least one of his members to begin the process of calling a vote to remove him.

After Representative Ken Buck, Republican of Colorado, surprised Mr. Johnson this month with an announcement that he was resigning imminently, the speaker said he did not expect more members to follow.

“I think, I hope and believe that that’s the end of the exits for now,” he said less than two weeks ago.