To be useful, a fiscal stimulus package should be implemented quickly and structured so that its effects on aggregate spending are felt as much as possible within the next twelve months or so. Stimulus that comes too late will not help support economic activity in the near term, and it could be actively destabilizing if it comes at a time when growth is already improving. Thus, fiscal measures that involve long lead times or result in additional economic activity only over a protracted period, whatever their intrinsic merits might be, will not provide stimulus when it is most needed... A fiscal program that increased the structural budget deficit would only make confronting those challenges more difficult.