Transcript for Pope's Unpredictability Complicates the Security Detail for His U.S. Visit
The Obamas and the Bidens took challenge. Security being beefed up in the three cities the pope will visit. Bomb-sniffing dogs outside the united nations in New York City. In Philadelphia, the city maps on surveillance cameras. Here in Washington, areas closed down in the shadow of the capitol. ABC's senior justice correspondent Pierre Thomas with the all-points bull tetin that went out to police. Pierre? Reporter: That's right, David. There's never been a security operation this size to protect one man on U.S. Soil. What makes this challenge unique is that this pope is unpredictable. As we saw in Cuba, a man nearly making his way to the pontiff. Security ripping him away. While there's no specific plot, police in Washington, New York and Philadelphia have done an assessment, looking at who might want to attack the pope. It ranges from Isis to mafia and, of course, loan wolves who could come out of nowhere. David? Pierre Thomas with us live in Washington, as well. Pierre, thank you.
This transcript has been automatically generated and may not be 100% accurate.