The dollar sold off and gold rallied on Monday, after Donald Trump ramped up his assault on the Federal Reserve by opening an unprecedented criminal investigation into the central bank and its chair, Jerome Powell. The US dollar fell some 0.36 per cent against a basket of major currencies, while the spot rate of gold climbed as much as 1.9 per cent as traders digested the President’s most dramatic salvo of a long-running feud with the Fed and its chair. Powell revealed that the US Justice Department had served the Fed with grand jury subpoenas…