Well, disasters and foreign economic threats aren't due to a politician's policy, and the regulatory environment usually doesn't change straight away (that requires legislation, not just a policy manifesto). War is a rare event as well, and it doesn't necessarily affect the wider economy - the war in Iraq and Afghanistan hasn't affected the US economy much, which quite happily went through a boom time in the early years of the war, then crashed for reasons unrelated to the war. Of course, the economy of Iraq got soundly fucked by war, but that wasn't due to the economic policies of the politician in charge.