The Risk of a Downgrade in the United States Credit Rating

In 2011, there was still a downgrade in the United States credit score. I think if Congress and the president do their jobs and get this done by the time they're supposed to, I think our credit rating is probably safe. If we go over the x-state, then I think all bets are off. But how would we know? Like what Yellen sort of just put out a statement saying, by the way, it happened.