Pittsburg: Donald Trump has made building a barrier to stop migrants on the US-Mexico border a central plank of his presidency, but on Wednesday, he came up with a puzzling new twist to the initiative: a wall in Colorado.

The problem? Colorado lies well within the United States, though its large southern neighbour New Mexico does border Mexico. "You know why we are going to win New Mexico? Because they want safety on their border," Trump said during a speech in Pittsburg.