Rep. Michael McCaul Fears an Attack Can Happen 'Anywhere, Any Time, Any Place'

The House Homeland Security Chairman talks to ABC News' Martha Raddatz

He expressed his concern about the growing rate of radicalization and recruitment online.

"We have about 200,000 ISIS tweets per day that hit the United States," he said. "The chatter is so loud and the volume is so high that it's a problem that's very hard to stop and disrupt in this country."

McCaul said there are active terror investigations in all 50 states, and there have been more than 60 ISIS-related arrests in the past year. While he commended the efforts of law enforcement, he said: "What keeps us up at night are the ones that we don’t know about, and I'm afraid that [Chattanooga] falls into that category."

In a press conference on Friday, McCaul called it "unacceptable" for military personnel to be killed at home after surviving tours of duty in overseas combat zones. After the 2014 shooting on Fort Hood he called for an end to the policy against against concealed carry on military facilities.

"It is just logical that we should provide them the means to defend themselves if they should be under any sort of attack like this," he said.