The Department of Justice has announced that it will treat the brutal murder of American journalist James Foley at the hands of ISIS as a criminal case.

Charles Krauthammer appeared tonight on “The Kelly File” to share his thoughts on this surprising news and how the U.S. should respond to Foley's murder.

"It is ridiculous to go back back to the pre-9/11 paradigm of treating acts of terror as criminal acts. They are not. They are acts of war against the United States," Krauthammer stated, comparing this development to FDR announcing the U.S. was going to track down the Japanese pilots behind the attack on Pearl Harbor.

"We have in ISIS an enemy that is armed, has a ton of money, a ton of recruits, controls an enormous amount of territory and has declared open war on the United States, of which the beheading of that American journalist was one instance," Krauthammer said.

He added that he does not think President Obama understands that the Defense Department not the Justice Department is our best hope against ISIS, since military intervention will be the only answer that ISIS respects.

Krauthammer concluded that the best response to Foley's beheading is a vigorous air campaign against ISIS, supporting non-American troops - such as Kurds and Iraqis - on the ground.

"That's the proper response, not sending a prosecutor over there to gather evidence about the beheading."

Watch the clip above.

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