The U.S. Postal Service is in trouble, and there’s no telling whether it will survive. It’s been battered by the Internet and a dragging economy, besieged by commercial competitors and stymied in its efforts to trim a costly web of post offices and delivery routes. On Aug. 1, it defaulted on a $5.5 billion payment to the U.S. Treasury for future retiree health benefits.Some think that it’s time to privatize the service, bringing an end to one of our oldest federal institutions.