According to Wikipedia contributors it is as follows:
The Bush Doctrine is a phrase used to describe various related foreign policy principles of United States president George W. Bush, created in the wake of the September 11, 2001 attacks. The phrase initially described the policy that the United States had the right to aggressively secure itself from countries that harbor or give aid to terrorist groups, which was used to justify the 2001 invasion of Afghanistan.
Later it came to include additional elements, including the controversial policy of preventive war, which held that the United States should depose foreign regimes that represented a potential or perceived threat to the security of the United States, even if that threat was not immediate (used to justify the 2003 invasion of Iraq); a policy of encouraging democracy around the world, especially in the Middle East, as a strategy for combating the spread of terrorism; and a willingness to pursue U.S. military interests in a unilateral way. Some of these policies were codified in a National Security Council text entitled the National Security Strategy of the United States published on September 20, 2002.
As to why Sarah Palin knows nothing of this, I have no clue. But the Republicans think she was their best VP pick so, whatever.
I guess this is just another reason to not vote for McCain.