Charles Krauthammer told viewers Monday on "Special Report with Bret Baier" that gun control and FBI investigations will not stop suspected terrorists from committing acts on U.S. soil such as the deadly Orlando nightclub massacre.  

Omar Mateen killed 49 people and wounded dozens more after opening fire with an assault rifle at the gay nightclub Pulse.  The gunman, who had pledged allegiance to the Islamic State, had been investigated by the FBI twice in 2013 and 2014. 

Krauthammer, a syndicated columnist and Fox News contributor, said intelligence investigations will help, but "in a country of this size with so many people as potential targets of investigation, unless you want to create a police state, there is no way that you can prevent" such attacks.

ISIS has repeatedly posted on the Internet urging supporters to kill Westerners wherever they could, but Krauthammer said that recruitment will go down only when ISIS is defeated.  

"Ultimately, the only way to decrease recruitment is not with logic, not with argument, not with really clever programmers who know how to do twitter," he said. "It is by defeating the jihadists or showing them in retreat."