Sanders has not had a single negative national news cycle his entire life, and he still only leads Trump by 6? Not impressive.
And yeah, Hillary has bounced back from high negatives before, and she can again... if she can make it to the general healthy.
The Republican attacks work on her cause she has been shown to be corrupt and not trustworthy. They are not working on Sanders. Everyone knows he's a democratic socialist so why would their minds change in November?
Sanders can't even get liberal policy wonks to back a lot of his plans. Do you really think he'll withstand a lot of scrutiny once the right-wing complex levels begins its attacks at him?
The right-wing is already attacking Bernie, and those Hillary hacks will let up on Bernie once he gets the nomination.