Bernstein draws a distinction between the parties:
[M]ost Democratic constituency groups have real policy demands, and that they're very eager to have those demands fulfilled. My sense is that a lot of Republican constituency groups have more symbolic demands.
Therefore, at the end of the day, a lot of Republican constituency groups are willing to go along with an all-or-nothing strategy on most issues, while Democratic constituency groups are perfectly willing to bargain for as much as they can get. Look: if you want universal health care, you are probably willing to settle for moving from 80% coverage to 95% coverage (or whatever the actual numbers are). If you believe that government involvement in health care is unconstitutional, or immoral, or whatever, then there's not much to bargain over.
He acknowledges that this is "a generalization that doesn't always hold, and probably an exaggeration" but he still thinks "it accounts for some key differences." But another way of looking at this is that the GOP is a theological movement, while the Democrats are a political one. Theology is about reiterating timeless truths - tax cuts are always good, regardless of circumstances, data, math, economics, etc; America can do no wrong, even if we do; anything gay is bad; spending must be stopped, except for Medicare, defense and that bridge down the street; climate change is untrue because liberals accept it, etc. Politics is about solving immediate problems while bribing your supporters.
When you look at it this way, you see the difficulty in compromising. How does the Pope compromise with an accountant? Until one side ceases to be grounded in magical/theological thinking, it's theater.