WASHINGTON — The fall of the Assad regime in Syria will not impact U.S. support, at least for now, for one of Washington’s most steadfast allies in the fight against the Islamic State terror group, according to senior American officials. Speaking just hours after Russian officials confirmed former Syrian leader Bashar al-Assad had fled Damascus and taken refuge in Moscow, and a day after rebel forces entered the Syrian capital, U.S. officials insisted there are no plans to alter the U.S. military footprint in Syria, which includes some 900 troops, most of them working in the country’s northeast with the