A whistleblower says the Postal Service is racing to launch an untested system that could block huge numbers of mail-in ballots, which is bad news for voters in states where mail voting is common.

• A new postal computer system rejects an entire batch of ballots if even one barcode fails to scan or match.
• One bad record in a batch of 10,000 could stop all the rest from going out to eligible voters.
• A federal judge blocked the plan, but the Postal Service is pushing ahead anyway, and the first mail ballots go out in North Carolina this week.
• The system came out of a Trump executive order letting agencies build citizenship lists and letting the post office refuse to mail ballots to anyone left off them.
• A third of American voters vote by mail, including many older Republicans, so the fallout may not land only on Democrats.

Outlook: The fight heads back to the Supreme Court, and until it rules the safest move for anyone waiting on a mail ballot is to plan to vote in person.