Of course they can. Budgets can always be revisited.
Political suicide. They barely have a majority. If I am not mistaken the military buildup and execution of the victory in the cold war was prosecuted in the 80s with a much larger Democratic majority. The White House is still run by the GOP, and that have essentially a 50/50 Senate on foreign policy with Lieberman. The Democrats simply do not have the capability to control things in the next six months.