KABUL, Afghanistan — Afghanistan’s embattled president left the country Sunday, joining his fellow citizens and foreigners in a stampede fleeing the advancing Taliban and signaling the end of a 20-year Western experiment aimed at remaking Afghanistan.The Taliban entered the capital early Sunday and an official in the militant group said it would soon announce the Islamic Emirate of Afghanistan from the presidential palace — a return rich in symbolism to the name of the country under the Taliban government ousted by U.S.-led forces after the 9/11 attacks. The official spoke on condition of anonymity because he was not authorized to...