The reason the frustrated are backing Trump is not that they like him, it's that we know what we're going to get with the others and IT HAS TO STOP or it will destroy our country as we know it. Trump might not be any better, but he sure as hell can't be any worse than what we've had. He's the hail Mary pass, lots of people are so disenfranchised now that they feel they have nothing to lose. That's why they're considering Trump.
I think this is as good of an explanation as any.
You didn't mention Cruz, but he is also seen as a part of the continuing establishment as well, just to a lesser degree.
Also, I do really think the issue of Canadian birth has had some level of negative effect as well with a portion of the voters.
