$14 Tr. or so in debt is the official or legal credit limit. But that is not the end of the story. What happens when you max out your credit? You can pay it off, bargain it down, go bankrupt, renegotiate terms for more time to pay it back etc.
In a prior post I dismissed the reality of the debt/deficit (not just for the US but for EU too).
Smart politicians will never let the debt become a real problem, i.e. where living standards of plummet as a result. Look at Greece! In Greece the games of politics and economics can hardly be played anymore. Politicians and journalists there can't scare citizens to vote for them against their opponents. They're not listening; just non-stop rioting against the starvation and privation. And economists can't convince anyone that suffering is in the national economic interest (whether it truly is or not is another question).
Point: US politicians won't let the debt reach the crisis point. Yes they will scare citizens to help them in the next election (the media will happily oblige). But to have it actually hurt! No. Put it off. Plenty of ways to do that (see above).