Krugman lays it out:

…know-nothingism — the insistence that there are simple, brute-force, instant-gratification answers to every problem, and that there’s something effeminate and weak about anyone who suggests otherwise — has become the core of Republican policy and political strategy. The party’s de facto slogan has become: “Real men don’t think things through.”

… remember this the next time someone calls for an end to partisanship, for working together to solve the country’s problems. It’s not going to happen — not as long as one of America’s two great parties believes that when it comes to politics, stupidity is the best policy.