CBS News correspondent Bob Orr reports on the tightest security for an inauguration - ever.
River and air patrols, bomb-sniffing dogs and undercover agents are all on guard - looking for anything resembling a threat.
A record crowd and the swearing-in of America's first African-American President presents a double worry for the FBI.
"We're asking our agents and our partners to go back, re-contact sources to ensure that we've scrubbed and re-scrubbed every potential threat that we have," says FBI Assistant Director Joseph Persichini.
A three-and-a-half square mile "Red Zone" from the White House to the National Mall to the Capitol is virtually locked down.
20,000 law enforcement officers will be backed up by more than 16,000 National Guard and active duty troops.
"We look at every type of threat out there whether we're talking about a simple lone individual type threat or something that is a more complicated, organized terrorist type event," says Mark Sullivan, director of U.S. Secret Service.
Those nearest to the swearing-in and those lining the parade route will be heavily screened and their movements restricted.
It would be impossible to run everyone through metal detectors, Orr reports, and spectators are expected to outnumber police about 100-to-1. Surveillance cameras will be critical in spotting potential trouble. Some 5,000 cameras spread all throughout the city will be piping real-time images into security command centers.
"It's gonna be constant information flow and constant on the ground eyes and ears," says Cathy Lanier with the Washington Metro Police Department
Officials say there is no known threat against President-elect Obama, but they recognize the inauguration is an attractive target.
"There's no question that an African American President will excite a certain small element of the population that's prejudiced or otherwise disturbed, or have an axe to grind," says Homeland Security Secretary Michael Chertoff.
Some people are griping about "security overkill," Orr reports. But, officials say they'll take the criticism rather than risk having to explain why something wasn't done.