Let's put his quote in context. He is asked what to do about the threat of future ISIS-inspired attacks in the U.S., and he says:
Well, the threat is pervasive on the Internet. Radicalization, not only foreign fighters coming back, but radicalization over the Internet which may have been the case here. They call it in law enforcement losers to lions that radicalize over the Internet. It's so pervasive -- 200,000 ISIS tweets a day, 1,000 investigations in all 50 States. It's really hard to stop all of it. But we have to get control over this Internet propaganda that is poisoning the minds of the United States.Losers to lions? I'd never noticed that expression before. But here's something from last February, and McCaul is doing the talking:
From “Losers to Lions” a term coined by some officials for people taking extreme measures and joining terrorist groups, in an effort to try to become something greater than themselves.... “They are usually not doing well in their lives, and are vulnerable to this sort of radicalization process and then they become what they think is a lion pulling off an act of terror,” said Congressman Michael McCaul who also serves as Chairman of the House Committee on Homeland Security.... “They want to become part of something bigger, and they think this is an adventure. ‘What's this Isis stuff all about?’ And they go on the Internet and they look at the videos,” Rep. McCaul said.
Those trying to leave the country to join Isis are not what is really concerning federal law enforcement as they can usually get them before they leave; it's those on U.S. soil in their homes. Christopher Combs is a Special Agent in Charge for the FBI in San Antonio. “Now with self-radicalization, with this home grown violent extremism, that's the kid in the basement who's doing it himself and wakes up one day and decides today is the day. That's hard, that's really hard for law enforcement to get in front of,’ he said.