Secretary of Defense James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE said Sunday “nothing keeps him awake at night,” and that he’s the one who keeps other people up at night.

“I keep other people awake at night,” Mattis told CBS’s John Dickerson on “Face the Nation.”

Mattis’s comments come as the U.S. faces a number of external threats from terror organizations as well as Russia.

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The Defense secretary said the U.S. is planning to accelerate its military strategy against the Islamic State in Iraq and Syria (ISIS), in the face of a growing number of attacks claimed by the group in western nations.

“Our intention is that the foreign fighters do not survive the fight to return home to North Africa, to Europe, to America, to Asia, to Africa. We're not going to allow them to do so. We're going to stop them there and take apart the caliphate,” he said.

The White House is grappling with a continuous series of bombshell revelations in the federal investigation into alleged ties between the Trump campaign and Russian election meddling.

Mattis addressed how the U.S. is dealing with Russia under the Trump administration.

“Right now, we're dealing with Russia, attempting to deal with Russia, under President Trump's direction, in a diplomatic manner,” the secretary said.

“At the same time while willing to engage diplomatically, we are going to have to confront Russia when it comes to areas where they attack us, whether it be with cyber, or they try to change borders using armed force,” he continued.