Open this photo in gallery: U.S. President Donald Trump holds a chart as he delivers remarks on reciprocal tariffs during an event in the Rose Garden at the White House, in Washington, on April 2.BRENDAN SMIALOWSKI/AFP/Getty Images African countries, highly vulnerable to U.S. tariff hikes and foreign-aid cuts, are hoping to placate President Donald Trump with a range of trade concessions, deportation deals and diplomatic manoeuvres. Unlike Canada or China, the African countries lack the economic clout to fight back with retaliatory tariffs. So they are experimenting with other tactics to persuade Mr. Trump to reverse a series of executive...