They write columns:
Advocates of changing the mission say it could leave around 60,000 troops in Iraq indefinitely (although the number could be much higher). The CBO evaluated a scenario that is consistent with this strategy at a cost of another $687 billion through 2017. And, since all of this is deficit spending, CBO projects that American taxpayers will spend an additional $152 billion in interest on this borrowed money by 2017.$687 billion could cover a lot of diabetes prevention programs.
As a member of Congress for 11 years and of the House Budget Committee for the last three, I can attest that such forecasts invariably underestimate the eventual cost and that the credibility of predictions from administration officials has been consistently unreliable.