Is the US safer from terrorism 20 years after 9/11?

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." Chertoff pushes back against the notion that the US government wasn't transparent enough about the intelligence it was collecting, and credits those efforts with foiling the plot to blow up airplanes mid-air from Heathrow to the US in 2006. Watch his interview with Ian Bremmer on this episode of GZERO World.