Updated

Charles Krauthammer told viewers Thursday on “Special Report with Bret Baier” that the shooting of four Marines in Chattanooga, Tennessee “is in all probability an example of radical Islam at work.”

However, he cautioned against overstating ISIS' influence on domestic attacks, noting that similar incidents, such as the 2009 Fort Hood shooting, predate the terrorist group.

The gunman in Thursday's attack, 24-year-old Muhammad Youssef Abdulazeez, was also killed. The investigation into the shooter's motive is ongoing.

"This is in all probability an example of radical Islam at work, and you know I think our emphasis on ISIS is a little overstated because we've had these attacks that predate ISIS," Krauthammer, a syndicated columnist and Fox News contributor, said.

"Nidal Hasan, when he shot and killed thirteen Americans, stood up on a table and yelled out “Allah Akbar,” [and] was acting pre-ISIS," Krauthammer said.

“What ISIS does is I think it gives direction, organization, and because of its command of the social media can actually activate people in a way that was more random before,” he said.

"But, the general issue is radical Islam. And unless we have a president who immediately says this is a lone gunman, how does he know?"