BAGHDAD (AP) — It is the modern era's military strategy of choice: overwhelming air power delivering precision-guided punishment backed by intelligence on the ground, with minimal exposure for soldiers of the striking side. Seductive though it is to risk-averse governments with war-weary publics, the approach has its limits — and these are on display in Syria and Iraq, where a U.S.-led coalition has carried out over 4,100 airstrikes against Islamic State radicals yet failed to stop the extremists. The Iraqi military was also to play a key role: air power would soften up the extremists, weakening them or getting them to flee, and the Iraqis were to deliver the final blow or retake areas abandoned by the militants. Iraqi security forces have poured resources and manpower into securing the refinery, and the militants stage periodic attacks on the complex. While air power has proven well-suited to hitting command-and-control centers, storage facilities and infrastructure, Islamic State fighters have proven adept at reacting. [...] for now, the Obama administration remains opposed to sending U.S.