Hit The Republicans Harder
Now this is more of the kind of thing we need to see. There are two strategies I think the contenders for the Dem nomination need to follow. (1) Compare and contrast themselves with their rivals without using Republican talking points (because doing so just makes the GOP's job easier in the general election), and (2) for every hit they make against a Dem rival, hit the Republicans ten times harder.
I don't usually applaud Sen. Biden, but he played this exactly right. When asked a question designed to get him to attack Hillary, he refused to take the bait and quickly pivoted into a strong assault against the leading Republican (Giuliani).
Hitting each other is fine. Politics is a contact sport. But always hit the Republicans even harder.