Add the Postal Service to the list of problems Congress is so far unable to fix. 

America's mail service endured its first-ever default overnight, failing to submit a required $5.5 billion payment for future retirees' health benefits by Thursday. 

The unprecedented lapse prompted new questions about the fate of the Postal Service as its financial situation spirals ever out of control, and Capitol Hill lawmakers have started a new round of fingerpointing after deadlocking over how to break the slide. 

"Congress must act quickly in order to prevent the loss of thousands of jobs in the Postal Service and the American mailing industry," Rep. Steve Cohen, D-Tenn., said in a letter to House Speaker John Boehner. 

The agency is expected to miss another $5.6 billion payment in September. For now, the missed mega-payments are not expected to affect day-to-day operations. An agency statement this week said the default would have "no material effect" on the Postal Service, affirming it would continue to deliver mail and pay employees as usual.