"Trump attorney D. John Sauer argued that presidential immunity means that a president cannot be prosecuted for any actions that fall under his presidential duties — unless the House first votes to impeach him and the Senate then convicts him." - WaPo

So, all he would have to do is find a "presidential duty" to kill off every Democratic and anti-Trump Republican senator after he is impeached by the House so that he cannot be convicted. There wouldn't ever be a trial.