I don't think he can. At this point his supporters won't take another Republican candidate so he's probably in it until the election unless he can say something that gets him tossed out. I think he's trying to make missteps all over the place so people see that he'll be a terrible global leader. Going to Scotland and somehow thinking they wanted to leave the EU and just having people protest him everywhere there seems to be more of a show than anything else just proving that he can't represent America on a global stage.