Because they wouldn't help his re-election by claiming something falsely against Biden, so instead trump tries to hurt them as revenge. What he usually does is escalate things for pr away from his bad press, and to flood the news as a distraction for control of the news cycle, and away from issues hurting him , like this virus and his allowing putin to have bounties on American service members , and away from Epstein and his connections with it. Lawrence O'Donalds show last night hit the nail on the head about why wasn't he asked about putins bounty on our service members by Chris Wallace on the Fox interview. trump hasn't said or tweeted about it too, which shows he knows if exposed that he could get badly hurt if she talks. She won't make to trial , and trump and Barr will make sure of that, and is using China now as a distraction. trumps threats now will escalate for pr he wants, and is getting more desperate and scared he will be exposed a lot more .