Recent events remind me of Cowen and Sutter's 1998's article on "Why Only Nixon Could Go to China." From the abstract: "Right-wing politicians sometimes can implement policies that left-wing politicians cannot, and vice versa. Contemporary wisdom has it that 'only Nixon could have gone to China.' The authors develop a model to explain this phenomenon."
Now Cowen and Sutter have a functionalist model where everythings happen for a good reason. But we can easily drop this Panglossian baggage. Let's suppose there is an Inane Policy that party X tends to favor. If party X pushes for it, though, party Y will make a big stink about it, and the Inane Policy will blow up in party X's face. So what hope does the Inane Policy have of coming to pass? Not much - unless party Y decides to give the Inane a chance.
I suspect that's what we're seeing now. If a Democratic president were backing a $700B bail-out, I have to think that Republicans would be crying "Socialism!" But if a Republican president does the same, the bail-out's natural enemies keep silent out of loyalty or ingroup bias. It's a lot like the contemporary Republican reaction to Nixon's price controls - if our boy is doing it, how bad can it be?
The scary thing is that once party Y gives the Inane a chance, party X may be able to finish the job without credible resistance. After party Y surrenders the rhetorical high ground by embracing the Inane, what's to stop party X from making Inanity a way of life?