'And Mexico will pay for it.'

Actually, 90% of presidential campaign promises are probably beyond the executive power. Buts it's certainly in a president's scope of authority to threaten another government to cut off trade and other incentives if they don't do x, y or z...in this case, building a wall.

For sure, I've just heard nothing but vagueness on that particular issue. BUT I'm just using that as an example. I think this is much more relevant in more local elections. Thanks for the comment!