[mikeash]

It leaves a record that the somebody else cast a vote. This would be noticed rapidly if the real person then showed up to vote and was prevented because an impersonator got there first. If that doesn’t happen, you can ask them if they voted. For people you can’t ask and know that they couldn’t have voted (for example, the record is stale and they’ve moved or died) then you know that any record of them voting must be an impersonator.

How often do any of these things actually happen? It’s all public record. The data is there for analysis. And yet nobody can point to more than a handful of examples.