Not very, according to Larison:
Except for Iraq, there isn’t a single U.S. military intervention abroad that Obama has not endorsed. He specifically cited the Balkan interventions in his Nobel Peace Price acceptance speech as examples of humanitarian intervention he supported. It isn’t just U.S. military action that he has routinely supported. As a Senator, he supported a resolution endorsing the Israeli campaign in Lebanon, and as President-elect he approved of Operation Cast Lead.