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Economists often use the cyclically adjusted budget deficit — an estimate of what the deficit would be at full employment — as a rough measure of how much fiscal stimulus the government is providing. By that measure, the federal government is now pumping as much money into the economy as it was seven years ago, when the unemployment rate was more than 8 percent.

The explosion of the budget deficit isn’t just a result of that tax cut. After Republicans took control of the House in 2010, they forced the federal government into austerity, squeezing spending despite high unemployment and low borrowing costs. But once Trump was in the White House, spending was suddenly O.K. again (as long as it didn’t help poor people). In particular, real discretionary spending — expenditures other than those on Social Security, Medicare and other safety net programs — has surged after years of decline.

So there’s really no mystery about the economy’s continuing strength: It’s a Keynesian thing. But what do we learn from the experience?

Politically, we’ve learned that the G.O.P. is deeply hypocritical. After all that Obama-era shrieking about the dangers of debt and the looming threat of inflation, the party cheerfully opened the spigots as soon as it had its own man in the White House. You still see news reports that describe prominent Republicans as “deficit hawks,” and puzzle over their relaxed attitude toward the current flood of red ink. Come on, everyone knows what that was all about.

Beyond that, we now know that the long period of high unemployment that followed the 2008 financial crisis could easily have been avoided. Those of us who warned from the beginning that the Obama stimulus was too small and short-lived, and that austerity was hobbling the recovery, were right. If we had been willing to provide the same kind of fiscal support in 2013 that we’re providing now, unemployment that year would probably have been under 6 percent, not 7.4 percent.