O n his high-stakes four-day state visit to the US, King Charles will have to walk a diplomatic tightrope as the guest of an erratic Donald Trump against the backdrop of Iran and security concerns after Saturday night’s shooting at the White House correspondents’ dinner . Many challenges lie ahead as he takes up his UK government-decreed task to “reaffirm and renew” bilateral ties amid a worsening “special relationship” on the 250th anniversary of American independence. Meanwhile, the ghost of Jeffrey Epstein and the shadow of the Sussexes are never far away. 1. Tricky visit with unprecedented degree of difficulty The contemporary political historian Anthony Seldon said the 27-30 April visit was “obviously beyond tricky” and had a “degree of difficulty” vastly surpassing any official visit since the first one by a reigning monarch, when George VI met Franklin D Roosevelt to persuade him to enter the second world war. “Because you are dealing with somebody who is so unpredictable,” Seldon said.…