Let me tag on some things: For his 1: We also have a massive breach of Benford's Law. Something used to determine fraudulent elections in places like Africa or South America. That right there is not just circumstantial, its damning..
Additionally, republican legislatures in Pennsylvania did try to prevent this. And with their ruling, their supreme court handed Trump a massively strong legal case.
In terms of Ohio and Florida, the primary fraud appears to be through mail in ballots. Both those states counted and tallied their mail in ballots prior to election day, only tabulating them ON the day. Compared to the other swing states which did all of it later. As to why not the senate, the simplest reasons are either A: They needed to do this fast or B: They wanted to avoid opening additional court cases against them.