Americans' discontent over the war in Iraq helped propel Barack Obama into the White House. U.S. forces now are preparing to leave Iraq next year, but they may remain in Afghanistan longer than many Obama supporters had hoped. In recent weeks, heavy resistance has delayed anti-Taliban operations. At the same time, relations between the United States and Afghan President Hamid Karzai remain tense, partly because of U.S. worries over corruption in his government. Overall, Afghanistan is proving a bigger challenge than Obama might have anticipated when he said a military surge now under way would be followed by a troop “drawdown” in July 2011. Meanwhile, Gen. David Petraeus, who replaced Gen. Stanley McChrystal as Afghanistan commander, said the drawdown will be gradual — and could even be postponed. Petraeus also said a potential new agreement could stretch out the Iraqi pullout deadline as well. Republicans generally back Obama's military commitments, but some Democrats are getting anxious.