So let's play this out. Do you really imagine that people are thinking along the lines of, "well, I'm struggling under loads of student debt, I just lost my job and have no health insurance, I'm worried about social security, and I know Bernie's been really hammering that he has a plan to deal with that, but dammit I'm so racist and homophobic and I hate immigrant children so much that I'll still vote for Trump even though he's going to screw me over in all of those areas?"
The danger is that the MSM will launch some unfounded smear against Sanders, similar to the Anti-Semitism smear against Jeremy Corbyn, and like said smear, it will stick. And so you'll get a whole whack of voters who will wind up thinking along the lines of "I know that a second Trump presidency will be worse for me than a Sanders presidency, but I can't vote for Sanders because (insert unfounded MSM smear here)".
That the MSM is going to launch a smear campaign against Sanders is a certainty. He is far more popular with people in the US than Corbyn ever was in Britain, and the attacks against Sanders just aren't sticking. Corbyn was also undermined by being unable to articulate a clear position on Brexit, which overwhelemed all the other issues in that campaign. There is no Brexit-like issue in the US that threatens to derail Sanders, and I really don't think that an anti-semitism charge is going to stick to a Jewish politician.