Why did the response to a depressed economy fall short? We can debate endlessly whether the Obama administration could have gotten a bigger, more sustained stimulus through Congress; what’s clear is that some officials failed to see the need for stronger policies. When Christina Romer, the administration’s top economist, argued for more stimulus, Tim Geithner, the Treasury secretary, dismissed it as “sugar.”

Beyond that, efforts to fight unemployment had to deal with a bizarre Beltway consensus that despite high unemployment and record low interest rates, debt, not jobs, was the real problem.

But the most important reason the great slump went on so long was scorched-earth Republican opposition to anything and everything that might have helped offset the fallout from the housing bust.

When I say “scorched earth,” I’m not being hyperbolic. Let’s not forget that in the summer of 2011 Republicans in Congress threatened to provoke a new financial crisis by refusing to raise the debt limit. Their goal was to blackmail President Barack Obama into cutting spending at a time when unemployment was still 9 percent and U.S. real borrowing costs were close to zero.

Now, Republicans claimed that their opposition to anything that might limit mass unemployment was driven by a deep commitment to fiscal responsibility. But this was complete hypocrisy — something that was obvious to anyone who looked at the actual content of G.O.P. budget proposals, which gave smoke and mirrors a bad name. You had to be extremely credulous to take fake G.O.P. deficit hawkery seriously; unfortunately, there were a lot of credulous pundits out there.

Anyway, the events of the past two years have made the reality of what happened crystal clear. The very same politicians who piously declared that America couldn’t afford to spend money supporting jobs in the face of a deep, prolonged slump just rammed through a huge, deficit-exploding tax cut for corporations and the wealthy even though the economy is currently near full employment. No, they haven’t abandoned their commitment to fiscal responsibility; they never cared about deficits in the first place.

So if you want to understand why the great slump that began in 2008 went on so long, blighting so many American lives, the answer is politics. Specifically, policy failed because cynical, bad-faith Republicans were willing to sacrifice millions of jobs rather than let anything good happen to the economy while a Democrat sat in the White House.

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