"Generic" always polls better than any actual person.
"Generic" is the ultimate hero who has no baggage or disapproval of any candidate & magically takes tremendous margins. Would be especially handy against someone as unpopular as Trump.
Anyways Other Data -
Male - Trump +5
Female - Sanders +15
18-29 - Sanders +23
Dems - Sanders +61
Ind - Sanders+9
GOP - Trump +57
Whites - Trump +3
African American - Sanders +53
Hispanic - +24
On Issues - Sanders has a wide lead in Healthcare, Education, Medicare/SS, Trump on Security, Economy is 50/50 odd. 18% of Hillary Clinton 2016 Voters are in Don't know while Bernie gets 76% of the Clinton 2016 vote.
How on earth does Trump have as much support from the GOP as Bernie has from the Democrats?
Biden for example is much ahead among Democrats vs Bernie which is boosting his numbers.
Whites only favoring the republican by 3? That would be the lowest GOP advantage with whites since 1996 (since 1964 if you don't count years when Ross Perot ran) and would go against the trend of white voters over the last several decades. I'm very skeptical, but this poll has lots of undecideds and a campaign would give republicans time to damage Bernie or whoever the democrat nominee is. Trump has already faced the full fledged attack of the democrats and the media for years. I do believe Trump would lose if the election were held right now, but I don't think these polls mean much.