As you note, the direct evidence is scarce... but with good reason. The Left, the MSM, the Dem machine, etc all have a heavily vested-interest in keeping it a secret. Literally trillions of dollars are on the line.
However, the anecdotal evidence is pretty massive on its own:
EVERY effort to clean up voter rolls: opposed by Dems
EVERY effort to ensure that only US citizens vote: opposed by Dems
EVERY time the number of votes in a district exceeds the actual number of registered voters (ie, a 100+% turnout): it is ALWAYS in a 90+% Dem district (and these are usually areas where you can't get a 10% turnout for free smoke-detectors).
EVERY time an election is close, the heavily Dem districts get reported last, and are almost always sufficient to turn the result into a Dem win, even if 90% of the other districts and counties vote GOP.
"It ain't rocket surgery"
“It ain’t rocket surgery”
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No, but it is brain science.