Probability of US default

Looks like we are on the verge of the unthinkable... a default by the US treasury. I always thought this was (and sure as hell hope it will be) an improbable event, especially since the US borrows in USD and owns the printing press that can print more of it. Kudos to partisan politics in making even an impossible (and undesired) event look highly probable. On the flip side, this situation makes it clear that history and common sense are bad precedents when it comes to rare events.