As I said before, Kamala is seriously fake and unlikable. All Trump has to do is convince a small % of voters in a few key states that they're voting for Kamala. It's guaranteed Trump is going to say in one of the debates "I really should be debating Kamala....".
And I'm not sure her record as a tough DA is going to excite the base, either. While poll after poll shows most people, across all segments, don't want to "defund the police", Kamala is going to have to walk what I think is an impossible line. She won't be a "tough on crime" asset - I think she's already apologized for that in the debates and she's only going to end-up distancing herself from that record further to placate the mob.
Then again, Trump knew Hillary. Everyone knew her. He was totally unprepared to attack Kamala today at his presser. That's par for the course, but it's not going to work on Biden who's generally well-liked and respected. And it won't work on Kamala because she's not that well known. He's going to have to actually have specific attacks with merit. And there's no evidence he's capable of that.