"So why is compromise so hard in the House?"

"Some commentators, especially liberals, attribute it to what they say is the irrationality of Republican members of Congress."

But the answer could be this instead: individual members of Congress are responding fairly rationally to their incentives. Most members of the House now come from hyperpartisan districts where they face essentially no threat of losing their seat to the other party. Instead, primary challenges, especially for Republicans, may be the more serious risk.