Where would Bernie be getting that close of a match-up?
It's obvious that the national polls have been meaningless junk for quite some time.
I can also imagine a scenario where people who have already voted for Clinton might now be saying they would vote for Bernie, on the basis that, now that they can't affect the result, they may as well support the guy they really support, rather than who they think can be elected.
A bit farfetched, so I pretty much agree that national polls are junk. Especially this one showing Trump dropping and Cruz rising, which is contradicted by just about everything.