Here's what Krugman wrote:
In fact, the trustees never said that waiting a year to "fix" Social Security costs $600 billion. Mr. Bush was grossly misrepresenting the meaning of a technical discussion of accounting issues (it's on Page 58 of the 2004 trustees' report), which has nothing to do with the cost of delaying changes in the retirement program.
Here, for the record, is the relevant excerpt from p. 58 of the trustees' report:
Between 2003 and 2004 it actually became less expensive to save social security until infinity time!