Why had the Democrats become so bitterly distrustful and battle ready?
Part of the answer is that more than perhaps ever before in modern times, the Republican party at the national level is controlled by extreme conservatives I call social fundamentalists who have no inclination to seek bipartisan consensus on anything. I remember a group of western Republican congressmen telling me early in my tenure at EPA that if they ever read a favorable editorial in The New York Times about the Bush administration's environmental policy, We might as well still have a Democrat president.
Here in the reality based community we hold these truths to be self-evident...
...but let a republican say it, and it's suddenly news.