Michael Hayden also believes Hillary Clinton's emails may have been hacked.

Former NSA and CIA Director Michael Hayden agrees that Republican presidential hopeful Donald Trump could be described as a recruiting sergeant for the Islamic State in Iraq and the Levant (ISIL, also known as ISIL).

"You don't have to be president ... to have already made Americans less safe," Hayden says.

The general also calls Hillary Clinton's use of a personal email account during her time as US secretary of state "inconceivable" and believes those emails may have been hacked.

"I would lose respect for scores of intelligence organisations around the planet if they weren't already thumbing through the emails," Hayden says.

The general adds he "would move heaven and earth" as the director of the National Security Agency to obtain unclassified emails of several foreign ministers.

Watch more of UpFront's wide-ranging interview with General Michael Hayden on Friday, April 1 at 1930GMT.

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Source: Al Jazeera