Federal authorities are mobilizing one of the largest security operations in U.S. history ahead of Pope Francis’s arrival Tuesday, an effort that is straining law enforcement resources in Washington, New York and Philadelphia. Hundreds of thousands of onlookers are expected to gather in all three cities for a glimpse of the Catholic Church leader, whose unrivaled global popularity and proclivity to wade into public crowds has added to security concerns.

Thousands of federal and local personnel will be deployed to keep the pontiff and the public safe. The challenges are immense. The pope’s five-day tour, his first in the United States, will include appearances at the White House and Congress, a parade on Constitution Avenue in Washington, a Mass at Madison Square Garden, a procession through Central Park in New York, and an open air Mass with up to 1.5 million people in Philadelphia. His Big Apple visit coincides with the 70th U.N. General Assembly, where more than 150 foreign delegations are also expected, creating a virtual lockdown in portions of midtown. FULL REPORT