Sometime in the spring the government will run up against its debt ceiling. This will prevent the government from any further borrowing.
Since the government has a substantial deficit, with spending exceeding revenue, hitting this limit would mean that the government would not have sufficient funds to pay for all its programs. It also would mean that the government could not pay interest or principle on debt that is coming due; in effect requiring it to default on its debt.
The prospect of the U.S. government defaulting on its debt creates the sort of end of the world scenario in which Congress rushed to pass the TARP in 2008. Back then, President Bush, Fed Chairman Ben Bernanke and all sorts of other luminaries told members of Congress and the public that we would have a second Great Depression if the Wall Street banks were not immediately bailed out, no questions asked. And the money flowed.
The prospect of defaulting on the debt will create a similar outbreak of shrill warnings of disaster. This would likely to lead to scenario in which President Obama signs whatever debt ceiling package House Republicans hand him, even if it includes the privatization of Social Security and Medicare and major cuts and/or elimination of other important programs. The argument from the administration will be that they have no choice.
I do not buy that this is going to happen, especially since any form of privatization would increase the deficit dramatically, but Baker is not the only one sounding the alarm.