[E]xperts, from both sides of the political spectrum, say the brutal experience in Iraq has eroded many elements of what has come to be called the "Bush doctrine," leaving the United States with less flexibility in the war on terror. ...[snip] The violent insurgency in Iraq, which has tied down 140,000 U.S. troops, has all but removed Americans' stomach for a similar pre-emptive engagement against an enemy who has not actually launched or prepared an imminent attack on the United States. Iraq "will leave a long and damaging legacy," said Fred Ikle, a senior government arms control expert for decades...