I have been following all this and looked at the litigation filed in Georgia by Powell. I have also been reading some of the more balanced/thoughtful commentary on it, both from Republicans and Democrats. In the interests of full disclosure/transparency, I am British, but of the two presidential candidates, I would personally lean more towards Trump - if I had to vote for one or the other.
I don't agree with the apparent general view here that the Trump claims are entirely a 'joke'. If the Powell filings are taken at face value, there is evidence to back up some of the more moderate claims being made by the Trump camp and also emanating independently from Powell, however it looks like they don't - so far - have before the court any evidence of actual specific acts of fraud. Rather, the allegations concern electoral irregularities and procedural lapses, and these seem to be an exceptional trend on a county-to-county basis in Georgia and not found across-the-board.
In Pennsylvania, the Republican-controlled state legislature (both House and Senate) has put a spanner in the works, but it appears the federal judiciary has knocked Trump back. The crucial issue there is whether state certification is solely for the state executive (under Democratic control) or for the legislature to override if the elections are 'contested elections', having issued Section 13, Article VII resolutions (as required under the Pennsylvania state constitution). One would need to look at Pennsylvania statutes and maybe common law on the question, as the constitution is silent on this specific point.
So far (my view may change with further developments), it does seem, at least to me, rather unlikely that Trump can upturn the whole election, due to the lack of specific evidence of fraud; but, one point that bears repeating is that Trump does not technically have to upturn the popular ballot. All he needs to do is cast doubt on the result in maybe two or three states that have sufficient Electoral College votes to drag Biden below the 270 threshold, as this would then (probably) force a contingent election in Congress.
Probably this rather extreme eventuality will not happen, but I am not dismissing the possibility altogether. It could happen. In any event, I think the whole thing will culminate in a showdown in the Supreme Court over the electoral methodologies of a handful of critical states, and that judgment will in effect decide whether the United States has to resort to contingent ballots in the legislature.