To understand this problem, consider everything that has to go right for Obama's strategy to work out. Success, as Obama defines it, means that Iraqi and Syrian forces have taken away ISIS's "safe havens" — or its control over territory. That means getting the local Sunni populations, who have thrown tacit support to ISIS, on board with pro-American Syrian rebels and the Iraqi government.
Even assuming the Iraqi and Syrian rebel forces can be made strong enough to take on ISIS in purely military terms, there's a list of everything that needs go right — politically — for Obama's strategy to work out: