Call it the liberal answer to the Laffer Curve:

But can the government afford this additional spending? The answer is yes. Despite the large federal deficit, global savers, including savings-hungry American households, are snapping up United States government securities at very low interest rates. And they will continue to do so as long as there is ample slack in the economy and inflation remains subdued. Over the next few years, there is little risk that federal deficits will crowd out private investment or precipitate a crisis of confidence in the American government, a spike in American interest rates or a sudden drop in the dollar.

On the other hand, as long as private demand remains weak, the risk is uncomfortably high that trying to reduce the deficit — by cutting spending or increasing taxes — will tip the economy back into recession or condemn it to years of faltering growth and debilitating unemployment. In fact, either outcome would depress tax revenue and could mean larger deficits.

UPDATE: Actually, we can take it even further. According to Laffer's logic, there is an optimal rate of taxation on the rich which will actually make them richer. This is the essential insight of Keynsianism: if the economy goes into protracted stagnation and retrenchment, corporate revenues cannot rise, or cannot rise as quickly as they might otherwise. Therefore, in order to continue to raise the after-tax income of the wealthy, it is imperative that we raise taxes on them now.

How's them apples?