A postal service truck rolls by a postal regional distribution center in Falls Church, Virginia.

The U.S. Postal Service is warning states it cannot guarantee that all ballots cast by mail for the Nov. 3 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 the agency, which has found 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 the coronavirus pandemic, which has led many Americans to consider voting by mail instead of heading to in-person polling places.