Did lots of people suddenly decide to vote in person, or were they ghosts that vanished in the morning light?
While we have come to expect such things from California, the state is far from the only one with problems. Nearly every "blue" state has refused to allow detailed inspection of its voter rolls. Why not? If there is nothing to hide, why wouldn't they welcome assistance in ensuring clean voter rolls? Many states accepted Federal assistance and even ones that thought they were clean found significant numbers of invalid registrations.
Just recently, Wisconsin has been diving deep into public records in search of fraud, not wanting to share the fate of its neighbor Minnesota. Those investigations have had an additional benefit of turning up ineligible voters to the point where applications for absentee ballots are down over 30% in key cities. Did lots of people suddenly decide to vote in person, or were they ghosts that vanished in the morning light?
So what do we do? One "good" aspect is that there will likely be many opportunities to observe cheating in its myriad forms, not just illegal voting, but also dead voters, votes recorded for people living elsewhere, improper ballot harvesting—the methods are legion and more than one will be used. To borrow from a Marine commander: "we are in a target rich environment".
For example, if you get a ballot for someone else, don't discard it. Give it to your local sheriff along with a statement of when you received it, and any supplemental information such as it is for a dead relative, or a prior resident. Each one of these statements and especially ballots is proof of an irregularity. Enough of these and an investigation will be required. Once is interesting, twice is coincidence, more is a pattern. The more problems found before the election is certified, the easier to challenge.
I mentioned the 20,000 non-citizens presented to California. In a way, I hope that it will be discovered that many of them already have votes recorded. Once a ballot envelope is opened and the ballot commingled with all the other ballots, it is impossible to correct the counts. Discovery of a significant number of invalid ballot receipts can invalidate an election.