Question: Why is there no "Obama Doctrine," some bold assertion of American military power in defense of our national interests? Other presidents, facing extraordinary challenges, have adopted "doctrines" that warned potential aggressors that they could go this far and no further.

For example, the Truman Doctrine in 1947: The US, President Truman stated, would protect Greece and Turkey against possible communist subversion or assault.

The Eisenhower Doctrine in 1957: The US, President Eisenhower proclaimed, would defend its friends in the Middle East who are threatened by Soviet expansionism.

The Carter Doctrine in 1980: The US, President Carter warned, would take military action to protect its oil supply lines through the Persian Gulf, should those supply lines be jeopardized, presumably by aggressive Soviet maneuvers.

These presidents all drew clear lines in the sand to warn potential aggressors that they would pay a heavy price for subverting or threatening America's national interests.