They asked it of the candidates during one of the 2016 debates.  I don’t remember the exact wording, but it was something like “Do you have anything good to say about your opponent?” Trump answered by talking about Clinton’s doggedness; she cited Trump’s attachment to family.  I’d say it’s an even bet that they ask it tonight.  If they do I hope Biden eschews faint-hearted praise and responds with something like this:

I suppose if I spent some time thinking about it I could find something good to say about Donald Trump, but I don’t think it would be anything really important.  The fact is that this is the most dishonest, the most corrupt, the most dangerous president in our history.  Whatever good there is in this man is overwhelmed by the bad.  That’s just the awful truth, and that’s what needs to be said.”