i don't know that it is the actual problem. the problem is people inflate things in their head because the idea of billions of dollars is so beyond their experience they think we spend a quarter on nasa, a quarter on foreign aid, a quarter on defense, etc (all of which are overstated) but they are asked this often individually and don't think about them in context of everything else. if you were to guess about something you really don't care deeply about you might make a guess of around that.
i don't think it's that they are all saying that trump is right, the media is wrong. i'm certain there is SOME of that, but it's not f**k half the country. it's mostly just not caring that much and how people answer polls. especially insidiously crafted polls like this one