The U.S. Postal Service is warning states that it can’t guarantee all ballots cast by mail for the November election will arrive in time to be counted, even if ballots are mailed by state deadlines. That’s raising the possibility that millions of voters could be disenfranchised. It’s the latest chaotic and confusing development involving an agency that now finds itself in the middle of a high-stakes election year debate over who gets to vote in America, and how. Those questions are particularly potent in the middle of a pandemic that’s led many Americans to consider voting by mail instead of heading to in-person polling places.