The CBO assumes economic growth will exceed 3 percent per year from 2012 to 2016 before gradually declining to a bit more than 2 percent in 2021. What if, instead, growth remains at 2 percent to 2.5 percent for the next decade? I asked Kogan to recalculate the budget numbers assuming a constant growth rate of 2.25 percent per year, which seems a plausible hard-slog scenario.

He found that the deficit then averages more than 7 percent of GDP. By 2021, it is more than 8.5 percent of GDP and increasing.

Under these modified growth assumptions, the cumulative deficit for the next decade is $13.7 trillion. In other words, the impact from sluggish growth on the budget shortfall over the same period exceeds $2.5 trillion — which is more than the roughly $2 trillion in deficit reduction that may wind up being agreed to as part of a deal to lift the debt ceiling.

(Failing to reach such a deal over the debt limit by early August, by the way, would lead to economic catastrophe and further cloud the unemployment outlook.)

If an extended period of slow growth is more likely than the official projections suggest, we’re in for a much nastier mix of high unemployment in the near term and large budget gaps over the medium term. This is only more evidence that the right policy response is a combination of more aggressive action to bolster the job market now and much more deficit reduction enacted now to take effect in a few years. On both strategies, we should be as bold as we can.