"The Democrats, and particularly Obama, have forced the Republican leadership into a corner . . .."
I disagree; Republicans wandered into that corner without help from anyone.
You're absolutely correct that the Republicans created the corner. What makes this situation unusual in my estimation is that Obama has actually backed them into it and called their bluff. This has never been his strategy before, and it's gratifying, but also quite surprising.
What America needs is a third party. Liberals, perhaps ...?