On the first question: One surprising thing about the debt obsession that peaked around 2011 is that it never had much basis in economic analysis. On the contrary, everything we know about fiscal policy says that it’s a mistake to focus on deficit reduction when unemployment is high and interest rates are low, as they were when the fiscal scolds were at their loudest.

The case for worrying about debt is stronger now, given low unemployment. But interest rates are still very low by historical standards — less than 1 percent after adjusting for inflation. This is so low that we needn’t fear that debt will snowball, with interest payments blowing up the deficit. It also suggests that we’re suffering from chronic weakness in private investment demand (which, by the way, the 2017 tax cut doesn’t seem to have boosted at all).

So in the past few months a number of prominent economists — including the former chief economist of the International Monetary Fund and top economists from the Obama administration — have published analyses saying that even now, with unemployment quite low, debt is much less of a problem than previously thought.

It’s still a bad idea to run up debt for no good reason — say, to provide tax breaks that corporations just use to buy back their own stock, which is, of course, what the G.O.P. did. But borrowing at ultralow interest rates to pay for investments in the future — infrastructure, of course, but also things like nutrition and health care for the young, who are the workers of tomorrow — is very defensible.

Which brings us to the question of double standards.

You don’t have to agree with everything in proposals for a “Green New Deal” to acknowledge that it’s very much an investment program, not a mere giveaway. So it has been very dismaying to see how much commentary on these proposals either demands an immediate, detailed explanation of how Democrats would pay for their ideas, or dismisses the whole thing as impractical. Was there the same pushback against Republican tax cuts? No.

Look, we’ve seen this over and over again — three times since 1980. Republicans rail against budget deficits when they’re out of power, then drop all their concerns and send the deficit soaring once they are in a position to cut taxes. Then when it’s the Democrats’ turn, they’re expected to clean up the Republicans’ red ink rather than address their own priorities. Enough already.

I’m not saying that Democrats should completely ignore the fiscal implications of their actions. Really big spending plans, especially if they don’t clearly involve investment — for example, a major expansion of federal health spending — will have to be paid for with new taxes. But if and when Democrats are in a position to make policy, they should be ambitious, and not let the deficit scolds scare them into thinking small.

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