Dick Cheney has been diagnosed with a blood clot in his left leg, leading to speculation he will be forced to resign as U.S. Vice-President. The 66-year-old has a history of major health problems, including four heart attacks, and has undergone quadruple-bypass surgery. He is a driving force in both the war in Iraq and the 'war on terror' and his resignation would be a huge loss to George Bush. The vice-president is the leader of Washington's neo-conservatives and is believed to be a dominant influence on Mr Bush's military and foreign policies.