US Republican leader Mike Johnson was set to face down critics Friday in a vote in Congress that could see him returned as one of the country’s top statesmen — or jettisoned to the back benches and political obscurity. If there is no speaker by Monday, Congress will not be able to certify Trump’s election victory and the Republican — who only gets one more term, having served in the White House from 2017-21 — will face delays in implementing…