Democrat Barack Obama and Republican John McCain fought a fierce political duel over Iraq Friday, in the latest testy escalation of their fast-evolving White House race.As Obama edged closer to the Democratic nomination, each man questioned the other's qualifications to serve as commander in chief, sparring over the US troop surge escalation strategy, and future of the war.The Obama camp pounced on a comment by McCain that the US troop garrison had already been pulled down to pre-surge levels, and complained the Republican used a picture of war commander General David Petraeus on a fundraising email.McCain said in a Wisconsin town-hall meeting on Thursday that "we have drawn down to pre-surge levels," then denied on Friday denied he had misspoken.