[ceejayoz]

I can't speak for California, but here in my area of NY you show up, give your name and address, which they find in the registered voters list, and you sign on an iPad that gets checked against the signature on file. Then you get handed a ballot. By the local volunteers who are mostly people from the neighborhood, plus observers from both major parties. Your neighbors are there checking in alongside you.

Getting past all this risks years in jail for... an extra vote in a safely blue state.

None of this requires an ID, in part because in the US, there's no law that you have to have an ID in the first place. "Papers, please!" used to be a derogatory thing about totalitarian regimes.

(More practically, if we Dems were rigging elections, we'd win more often.)

[wat10000]

If the person you're impersonating shows up to vote too, then that will be noticed and there will be questions. If they don't, there are still opportunities to notice issues after the fact. Get a list of who voted, call a random sample and ask if they actually voted. Check for dead people or noncitizens.

There isn't a ton of checking in advance but that doesn't mean we can't know if the results are legit. If there was a concerted, large-scale effort to impersonate voters, it could be done, and it would seriously screw things up. But it would not go undetected.