For Michael Chertoff, former US secretary of Homeland Security from 2005 to 2009, the fact that America has not experienced a single attack by foreign terrorists since 9/11 proves that the US was "successful" in its strategy to prevent terrorism. That "was not [an] accident and there was a deterrent effect to be honest — had we been lax, more would have tried." Although he admits the US government wasn't transparent enough about the intelligence it was collecting, Chertoff credits US intelligence agencies with helping to foil the plot to blow up airplanes mid-air from Heathrow to the US in 2006. The US mission in Iraq, or what came after was not clearly thought out, according to Michael Chertoff, who served as the Secretary of the US Department of Homeland Security under George W. Bush. The Iraq war made it difficult to focus on the US mission in Afghanistan and absorbed resources that could have been used more effectively elsewhere, he said.

Watch this episode of GZERO World with Ian Bremmer: Is America safer since 9/11?