Same day voting is heavily republican and mail/absentee is heavy democratic. That is why you hear people referring to the blue and red mirages. Some states are slow or dont count the latter until during or after election day while other states are ahead of it and have it already done by the time the polls close. It is up to each state and county to work it out based on the laws. This is why you saw trump far ahead in some states, and biden far ahead in others, but as both votes are finally combined, it is a lot closer.
Generally speaking, the US likes keeping whoever the incumbent is. Unless it is a large wave year, incumbents are safe. In my lifetime, every president has been elected to 2 terms.(tbd this election) Similar for senators in my state.(only 3 total, 1 of which retired)
Referring to the posts above about Tx and GA. republicans have won the popular vote nation wide once since 2000. The electoral college has saved them here. States that have a lot of hispanic votes could be what decides future races in the southern states. On the flip side, democrats have to keep an eye on the rust belt. It has imo been leaning more and more republican. I know my state went from a purple to a lean red. Who knows where we will be in 10 years, with all the demographics shifts.
I doubt a recount shifts a vote total much. You would need a lot of ballots to be tossed out to make a difference. Of course any court decisions could add or remove some. 20K is a lot to make up though.
I think both parties need to move back to the center, if they want to have a chance at flipping any states or seats. The more polarized it gets, the fewer states that matter.