Check the news or the Tweeters today... He must've read that, or the bozo who asked him the question and put the idea in his head did. He's going on TV tonight. #BoycottTrumpPrimeTime is the number one trend on Twitter.
Like a disturbing number of Trump's worst musings, the entire idea of "declaring an emergency" to make his wall happen was 100% the brainchild of press reporters who asked Trump about the possibility completely out of the blue, with no prompting whatsoever. Before a reporter asked that, he'd never suggested anything about declaring an emergency, nor had any White House sources suggested that it was internally being considered. I'd lay odds that Trump didn't even know the avenue existed, and would never have known, if not for the press volunteering the possibility to him in the form of a loaded question.
I've hinted at it already, but it's becoming increasingly obvious to me that Trump is actively, intentionally being trolled into making some of his most offensive, provocative, ignorant, and legally dubious statements and policy explorations not by the workings of his own feeble and depraved mind, or by his kids, or his advisors, or his political lackeys; but rather by media introducing concepts and possibilities to him in the form of pointed and loaded questions. And as I've said before, it's not just Fox News doing it, either.