Former US President Bill Clinton should not have been impeached for his affair with Monica Lewinsky, but for lying in an earlier sexual harassment case, former House Speaker Newt Gingrich has said. Gingrich led the 1998 impeachment of Clinton, in which ‘Slick Willy’ was charged with – and acquitted of – lying under oath and obstruction of justice. The charges centered on Clinton claiming that he “did not have sexual relations with” White House intern Monica Lewinsky, which he did. Speaking to New York Post columnist Miranda Devine on Tuesday, Gingrich said he now considers the decision to impeach Clinton over the Lewinsky affair to be “a mistake.” “I think it was a mistake because the real problem wasn’t Lewinsky,” he said. “The real problem was he had committed perjury in a case involving sexual harassment while he was governor.…