ANKARA, Turkey — Turkey rallied behind Prime Minister Recep Tayyip Erdogan in his blistering condemnation of Israel after its commando raid on an aid ship to Gaza. But as dust settles from the May 31 attack, Turkey's resurgent opposition seems to be gaining traction by articulating fears that Erdogan is steering NATO's only Muslim member away from the West, jeopardizing EU membership efforts, and even undermining a long-running battle against separatist Kurds. The views of the Republican People's Party — which considers itself a guarantor of secular values and enjoys a power base among Western-leaning urban elites — are increasingly...