The day started with a social media post that sent shockwaves around the world. Here was a sitting president of the most powerful country on earth threatening to wipe out Iran. "A whole civilisation will die tonight," he wrote, "never to be brought back again". In Washington, the condemnation came thick and fast. "Unhinged," "deranged," "lunatic," "genocidal" were just some of the adjectives deployed by his political opponents, many of whom called for his ouster. He was an "extremely sick person," according to the most senior Democrat in Congress, Chuck Schumer. Many Republicans, on the other hand, played down the…