What I was more particularly thinking of was his accusations (without a shred of evidence) that various public officials had knowingly acted dishonestly ('fraudulently') in deliberately fiddling the count / voting figures for the 2020 presidential election.
He has named specific people, and accused them of, not just incompetence, but of committing specific criminal offences. That sounds like libel / slander (dunno which, if it's a tweet) and if I were one of those officials, I'd want to sue him for defamation because my professional reputation would have been jeopardised.
It would be as if, in my local newspaper, I published a claim that 'In the last general election, Mr Fred Smith, the returning officer for the South Hereford parliamentary constituency, deliberately falsified the result by deliberately hiding / destroying 500 perfectly valid votes'. That is of course libellous, and I would never get away with it. Mr Smith would be fully entitled to sue me personally and sue the newspaper.
Although it would never happen because no newspaper would ever be so foolish as to publish such a blatant libel. Tweets, however, as we are all acutely aware at present, are not subject to the same editorial discipline.