Statistical analysis.
In short, this was a signifcant mail-in election.
People requested ballots.
Lets assume a blue state… 70% request ballots.
Of those 60% are Ds and 40% Rs (ignore Indies for sake of example).
Turns out 85% of D's return their ballots, vs 80% of R's.
No biggie, right?
Well, what if on a county-by-county basis, the numbers are pretty even for D's … still ~85%, But for R's the return rate is 85%, except for 4 where the return rate is 75%; big counties, so it drags down the average.
Note I'm not even suggesting a higher-than-normal rate of return for D's, just an anomoly that needs to be explained over R ballots.
So, let's dig into precinct-by-precinct in those 4 counties…
Oh, odd, in 12 of them NO R ballots were returned.
See?