My reading of what the ratings agencies have said is that if the GOP somehow manages to force the Democrats to do everything their way, this will not secure our AAA; it will guarantee that we lose it, because it will show that we are currently unable to make the ugly bipartisan compromises that long-term budget balance requires, and raises the risk that sometime in the not-very-distant future, the other party will retaliate by threatening default. That's what Wall Street cares about. Not saving social security. Not lower spending. They just care about getting enough consensus to keep the checks flowing.
I think it is easy to over-estimate ideology among members of wall street because a few of them have decided to spend their wealth on political activism. But, for most businesses (especially in banking), the goal seems to be getting paid and it is worth remembering that. Narrowly averting a disaster is only of limited value if structural incentives (and poor journalism) ensure that it happens again and again.