But the PROBLEM with projections is that they are based upon assumptions which may not occur. And IF the projection is created based upon wishful thinking, or some underlying agenda, the probability may be quite high that the assumptions will not occur.
All the historical data I see suggests that we are adding debt at a rate of about 7% of GDP per year. Unless GDP is growing much faster than 7%, or someone has decreased the Federal outlays, the deficit will continue to grow.
I think Krugman's graph is projecting an uptick in GDP as if it is a permanent growth trend, i.e deducing that a change from 1% GDP growth to 3% GDP growth is a trend and projecting it to 5%, 7%, 9%, 11%, etc. - until the growth overpowers the spending.
I doubt that anyone who has ever met a budget in the real world would project that rising income would overwhelm unbridled spending. But the analysis gives Democrats a little more time to avoid accountability, and that seems to be their main goal: "steal all we can while we can, then blame the problem on the other guy".
I think that you put your finger on it. This country has always managed to outgrow its debt problems, and Krugman just naturally assumes that this will continue to happen in the future. What we need to factor in is the effects of higher taxes, Obamacare, higher energy costs, greater regulations, rules which strengthen organized labor, etc. (In short, the Obama Administration) will have on growth rates going forward. I believe that I am on solid ground in predicting these aforementioned policies will dampen economic growth in this country. In fact, I cannot see how they will not. Growth projection greater than 2 or 2.5% are overly optimistic. We could barely achieve 2% growth when we were coming out of a recession, and that is when growth rates are likely to be their highest. So, no, growing out of our current debt problems are exceedingly unlikely, especially when debt growth continues to outpace GDP growth.