What's really interesting is that the [manufactured] debt ceiling crisis in 2011 caused the credit rating agency S&P to downgrade US debt then as well...BUT, instead of causing US debt to be more expensive, investors wound up selling equities and buying MORE debt, causing interest rates to go down even more, and bond prices to increase!
Bill Gross, founder and manager at the time of PIMCO's fixed income/debt fund, the biggest in the world, wagered HEAVILY that the debt downgrade would cause interest rates to go UP, and bond prices and to go down, as they should, according to every economics textbook ever. He lost billions as a result and I think that's about when Pimco fired him even though he was the founder.
Interestingly, this downgrade seems to be largely ignored by both debt and equity markets. Markets appear to be pricing this in as "business as usual" which is sorta interesting in itself. Smart money seems to think everything is fine. I usually go with the smart money on these things, so I'm not too upset about Fitch's downgrade. (Just to be clear though, the R party can go fuck themselves.)
That's always possible I suppose but I don't think so. The crisis in 2011 rocked markets for months with monstrous daily swings up and down. There was barely a blip when fitch downgraded the debt and during the last few debt ceiling impasses.
Personally I think it's pretty clear at this point that it is just theater and they'll never allow a default. The reason being, all of congress is too wealthy and heavily invested in stable world markets, and obviously in the pockets of their corporate overlords who feel the same. A default would be catastrophic so it's just not going to happen.