The bottleneck is not necessarily the U.S. Postal Service, but rather the state and local election officials who set arbitrary deadlines for postmarking ballots, and who will have to sort out millions more additional mailed ballots than they are used to handling. In many states, they have never done anything like it before.
In New York’s Democratic primary, more than one out of every four vote-by-mail ballots was disqualified. In Clark County, Nevada, 223,000 mailed ballots were returned as undeliverable. That is not a postal problem; it is a government problem that cannot be fixed by November.
But given that the Obama-Biden administration itself removed thousands upon thousands of mailboxes, this is a conspiracy theory that — like the others — has gone bust, at least for those of us living in the real world.