Why did government spending rise so much under Reagan, with his small-government rhetoric, while shrinking under the president so many Republicans insist is a secret socialist? In Reagan’s case, it’s partly about the arms race, but mainly about state and local governments doing what they are supposed to do: educate a growing population of children, invest in infrastructure for a growing economy.

Under President Obama, however, the dire fiscal condition of state and local governments — the result of a sustained slump, which in turn was caused largely by that private debt explosion before 2008 — has led to forced spending cuts. The fiscal straits of lower-level governments could and should have been alleviated by aid from Washington, which remains able to borrow at incredibly low interest rates. But this aid was never provided on a remotely adequate scale.

This policy malpractice is doing double damage to America. On one side, it’s helping lose the future — because that’s what happens when you neglect education and public investment. At the same time, it’s hurting us right now, by helping keep growth low and unemployment high.

We’re talking big numbers here. If government employment under Mr. Obama had grown at Reagan-era rates, 1.3 million more Americans would be working as schoolteachers, firefighters, police officers, etc., than are currently employed in such jobs.

And once you take the effects of public spending on private employment into account, a rough estimate is that the unemployment rate would be 1.5 percentage points lower than it is, or below 7 percent — significantly better than the Reagan economy at this stage.

One implication of this comparison is that conservatives who love to compare Reagan’s record with Mr. Obama’s should think twice. Aside from the fact that recoveries from financial crises are almost always slower than ordinary recoveries, in reality Reagan was much more Keynesian than Mr. Obama, faced with an obstructionist G.O.P., has ever managed to be.

More important, however, there is now an easy answer to anyone asking how we can accelerate our economic recovery. By all means, let’s talk about visionary ideas; but we can take a big step toward full employment just by using the federal government’s low borrowing costs to help state and local governments rehire the schoolteachers and police officers they laid off, while restarting the road repair and improvement projects they canceled or put on hold.