By ABDI LATIF DAHIR and ERIC SCHMITT The barrage of airstrikes launched by the United States across Syria late Friday underscored the challenges facing the country’s president, Ahmad al-Sharaa, as he struggles to assert control over the nation and navigate a nascent relationship with President Donald Trump. U.S. fighter jets, attack helicopters and artillery struck more than 70 suspected Islamic State positions across central Syria, targeting the group’s infrastructure and weapons sites,...