ISTANBUL — President Recep Tayyip Erdogan’s party on Sunday was facing defeat in local elections in the Turkish capital, Ankara, and possibly even Istanbul, its largest city, a result that shook the nation as Mr. Erdogan suffered the first major electoral setback of his decade and a half in power.The municipal balloting around the country came nine months after national elections that extended Mr. Erdogan’s hold on power. It was closely watched as a barometer of his standing with voters after Turkey’s economy fell into recession and he assumed sweeping new executive powers.Mr. Erdogan claimed victory over all in the...