Appropriations Override Possible?

From Robert Novak:

Democrats are plotting a rapid override of three expected vetoes of spending bills by George W. Bush, who did not veto a single bill until his sixth year as president. ...

The third attempted override would involve a contemplated merger of Defense appropriations with spending for Labor and Health and Human Services [which includes Social Security]. That package would contain so many pet earmarks for individual lawmakers that it would be difficult to sustain a veto.