is it possible for a country to max out its credit?

Sure, just look at Greece. And since they use the Euro they can't print more money.

Also, printing more money won't necessarily fix a credit crisis. It will allow you to pay off existing debt, but not necessarily borrow more money (lenders aren't complete idiots).

No, it isn't. Countries (most of them) PRINT THEIR OWN money.

The USA could theoretically retire its entire debt just by printing enough cash THIS WEEK to cover all future Bond payments that will eventually be due on outstanding Treasury Bills/Bonds, but that would serve NO purpose....

National debt consists in issuing bonds which pay the bearer their initial investment back over time, with interest. People* buy them VOLUNTARILY because they are a safe & reliable. Government ISSUE them because it's a cheap way to get "up-front" cash to run the country, rather than "saving up" each time we need to buy some new tanks, build a new highway, or some schools, or a rocket to go to Mars in...