Capitol Invasion by Lone Gunman Could've Been al Qaeda

How could it happen? One lone individual with a gun entered the U.S. Capitol building with ease. Are we to believe that the U.S. government is ready to defend us from terrorism when it can't even stop one madman?:

"A gunman crashed a stolen vehicle into a police car outside the U.S. Capitol on Monday and then raced through the heavily fortified building before being arrested by a swarm of law enforcement officers."