The Republican majority in the US House of Representatives is set to dwindle further with the early exit of Mike Gallagher of Wisconsin, once a rising star of the party. A former US marine who twice deployed to Iraq, Gallagher, 40, is a relatively moderate voice in party at the mercy of the far right. He had already announced his decision to retire but in a statement on Friday he said: “After conversations with my family, I have made the decision to resign my position … effective 19 April. I’ve worked closely with House Republican leadership on this timeline.” The announcement came shortly after Marjorie Taylor Greene of Georgia, an extremist even in a party held hostage by its far right, responded to the passage of a Democrat-backed funding bill by filing a motion to remove Mike Johnson, the speaker from Louisiana. Allies said Gallagher was pushed to the exit by such behaviour, according to Politico, particularly the right’s ejection of Johnson’s predecessor as speaker, Kevin McCarthy, last October. Friday was also the last day in Congress for Ken Buck of Colorado, a rightwinger nonetheless disillusioned by intra-party chaos who also chose to bring forward his intended retirement. After Buck’s departure, Republicans will control the House 218-213. Once Gallagher is gone, Johnson will only be able to afford to lose one vote if Democrats hold together. Under Wisconsin elections law, Gallagher’s seat will not be contested until November. On Friday, Steve Scalise of Louisiana, the majority leader, told reporters: “It’s tough, but it’s tough with a five-seat majority, it’s tough with a two-seat majority, one is going to be the same. We all have to work together. We’re all going to have to unite if we’re going get some things done.” In a caucus dominated from without by Donald Trump, the presumptive Republican nominee for president, that seems highly unlikely. Last month, Gallagher was one of three House Republicans who voted against the impeachment of Alejandro Mayorkas, the homeland security secretary, an effort widely seen not to meet the threshold for charges of high crimes and misdemeanours but meant to boost Republican messaging on immigration in an election year. Mayorkas will almost certainly escape conviction and removal by the Democratic-held Senate. Soon after voting against the Mayorkas impeachment, Gallagher announced his plan to retire. “Electoral politics was never supposed to be a career and, trust me, Congress is no place to grow old,” he said. “And so, with a heavy heart, I have decided not to run for re-election.” On Friday, Gallagher cited his work chairing a select committee on China and said “four terms serving north-east Wisconsin in Congress has been the honour of a lifetime and strengthened my conviction that America is the greatest country in the history of the world”.