By Paul Krugman. New York Times.

John Boehner was a terrible, very bad, no good speaker of the House. Under his leadership, Republicans pursued an unprecedented strategy of scorched-earth obstructionism, which did immense damage to the economy and undermined America’s credibility around the world.

Still, things could have been worse. And under his successor they almost surely will be worse. Bad as Mr. Boehner was, he was just a symptom of the underlying malady, the madness that has consumed his party.

For me, Mr. Boehner’s defining moment remains what he said and did as House minority leader in early 2009, when a newly inaugurated President Obama was trying to cope with the disastrous recession that began under his predecessor.

There was and is a strong consensus among economists that a temporary period of deficit spending can help mitigate an economic slump. In 2008 a stimulus plan passed Congress with bipartisan support, and the case for a further stimulus in 2009 was overwhelming. But with a Democrat in the White House, Mr. Boehner demanded that policy go in the opposite direction, declaring that “American families are tightening their belts. But they don’t see government tightening its belt.” And he called for government to “go on a diet.”

This was know-nothing economics, and incredibly irresponsible at a time of crisis; not long ago it would have been hard to imagine a major political figure making such a statement. Did Mr. Boehner actually believe what he was saying? Was he just against anything Mr. Obama was for? Or was he engaged in deliberate sabotage, trying to block measures that would help the economy because a bad economy would be good for Republican electoral prospects?

We’ll probably never know for sure, but those remarks set the tone for everything that followed. The Boehner era has been one in which Republicans have accepted no responsibility for helping to govern the country, in which they have opposed anything and everything the president proposes.

What’s more, it has been an era of budget blackmail, in which threats that Republicans will shut down the government or push it into default unless they get their way have become standard operating procedure.

All in all, Republicans during the Boehner era fully justified the characterization offered by the political analysts Thomas Mann and Norman Ornstein, in their book “It’s Even Worse Than You Think.” Yes, the G.O.P. has become an “insurgent outlier” that is “ideologically extreme” and “unmoved by conventional understanding of facts, evidence and science.” And Mr. Boehner did nothing to fight these tendencies. On the contrary, he catered to and fed the extremism.

So why is he out? Basically because the obstructionism failed.

Republicans did manage to put a severe crimp on federal spending, which has grown much more slowly under Mr. Obama than it did under George W. Bush, or for that matter Ronald Reagan. The weakness of spending has, in turn, been a major headwind delaying recovery, probably the single biggest reason it has taken so long to bounce back from the 2007-2009 recession.

But the economy nonetheless did well enough for Mr. Obama to win re-election with a solid majority in 2012, and his victory ensured that his signature policy initiative, health-care reform — enacted before Republicans took control of the House — went into effect on schedule, despite the dozens of votes Mr. Boehner held calling for its repeal. Furthermore, Obamacare is working: the number of uninsured Americans has dropped sharply even as health-care costs seem to have come under control.

In other words, despite all Mr. Boehner’s efforts to bring him down, Mr. Obama is looking more and more like a highly successful president. For the base, which has never considered Mr. Obama legitimate — polling suggests that many Republicans believe that he wasn’t even born here — this is a nightmare. And all too many ambitious Republican politicians are willing to tell the base that it’s Mr. Boehner’s fault, that he just didn’t try blackmail hard enough.

This is nonsense, of course. In fact, the controversy over Planned Parenthood that probably triggered the Boehner exit — shut down the government in response to obviously doctored videos? — might have been custom-designed to illustrate just how crazy the G.O.P.’s extremists have become, how unrealistic they are about what confrontational politics can accomplish.

But Republican leaders who have encouraged the base to believe all kinds of untrue things are in no position to start preaching political rationality.

Mr. Boehner is quitting because he found himself caught between the limits of the politically possible and a base that lives in its own reality. But don’t cry for (or with) Mr. Boehner; cry for America, which must find a way to live with a G.O.P. gone mad.