ISIS claimed responsibility last week after two men opened fire at a Muhammad cartoon contest in Garland, Texas. Now, the terror group claims it has recruits across the U.S. who are ready to attack.

Chairman of the House Homeland Security Committee Michael McCaul joined Chris Wallace on "Fox News Sunday" to discuss the threat of a homegrown terror attack.

"I think there’s been an uptick in the threat streams out there, the level of chatter, Internet calls to arms, if you will, to light up potential ISIS followers potentially in the United States, and attack military installations," McCaul said. "We are seeing these directives almost on a daily basis. It's very concerning."

"Really, terrorism has gone viral."

McCaul said the two main threats are foreign fighters coming out of the war region in Iraq and Syria and the thousands of people already in the U.S. who will take up the call to arms when ISIS sends out a tweet or message to followers.

"This threat is like finding a needle in a haystack sometimes. And it's going to get worse and not better."

Watch the full "Fox News Sunday" interview above.

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