George W Bush and Bill Clinton both took apparent jabs at Donald Trump at a forum on Thursday night as they named the one characteristic a president needed above all others. The two former presidents were speaking at a graduation ceremony for the Presidential Leadership Scholars program at the George W Bush Presidential Center in Dallas. Bush replied ‘humility’ in answer to the question about presidential qualities, and added – ‘I think it's really important to know what you don't know and listen to people who do know what you don't know.’ Clinton said anyone holding the highest office in...