Trump wants impeachment to seem like it's about race rather than collusion and obstruction.
Trump can't defend himself against collusion and obstruction attacks by Dems. Most Republicans and other Trumpies didn't commit obstruction or collude with Russians. Trump did. He's not in the same boat as his followers when it comes to Russian collusion and obstruction of justice.
To get his followers to defend him at maximum enthusiasm, Trump knows he needs to get them defending not just him but themselves. He does that by stirring up interracial resentment. If Trump can get Dems to seem like they are impeaching him to punish him for his racist behavior, he maximizes his likelihood of success. Many of his supporters respond to racial resentment. They'll vigorously fight impeachment if it is about that.
Trump's trying to distract and drag the fight to better ground for himself. Imo, sure, we should be fighting his racism head on, but we should not forget the many other impeachable offenses he committed. When we're countering one of his little racist barbs, we should bring up the other things he's done too and suggest he might be trying to distract from them.