@bobsal u1553115,
The polls showing Bernie beating Trump by a slightly wider margin than Hillary beats Trump do not take into account that the Republicans have spent very little time criticizing Bernie at all. They have put all their effort into an all-out assault against Mrs. Clinton, whom they do not want to face in November and would like very much to see beaten by Bernie.
Then if Bernie gets the nomination, we are going to hear all about the Socialist Workers Party and Communist ties and whatnot in his background. They're not mentioning it now because they greatly desire that Bernie beats Hillary.