Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

What is the rationale behind stock markets retreating due to S&P having a negative outlook on the USA?
If you spoke in front of a group of people in 2001 about the possibility of be lowered, you would be written off as a kook. Now S&P is talking about a negative credit outlook -- scary stuff. It's scary because a base assumption in any risk model is that US Treasury debt is utterly reliable and comes with zero default risk. So publicly banding about the notion that US Treasury debt may be less the AAA in two years is a shock to the system and changes the way many people assess risk. It's also scary because Treasury debt is auctioned... will a spooked market still accept a measely 2.9% return for a 7 year T-Bill? But while the prospect of a credit downgrade is truly a bad thing, you also need to take the S&P statements with a grain of salt -- since being a named a villain during the mortgage implosion (these were the guys who declared junk mortgage securities as AAA), they now err on the side of doom and gloom. So while things are bad, they've been bad since the Bush administration was forced to put Fannie Mae & Freddie Mac on the government balance sheet to stave off a bank panic. The scary stuff about default in July due to the debt ceiling debate is not very credible at all. Unless the Republican House plans on dramatically slashing spending on Medicare, Defense or Social Security and have the votes to stick to that strategy, the debt ceiling will be raised after much ado. Politicians talk tough, but have a proven track record of creating financial problems tomorrow to fix electoral problems today.