An army of police, Secret Service agents and military personnel will keep a close eye on President-elect Barack Obama as he utters the 39 words that officially will make him the nation's 44th president.
Security for Tuesday's inauguration is likely to cost more than ever before, with military jets canvassing restricted airspace and armed helicopters at the ready. With more than 8,000 police and an estimated 11,000 military personnel and thousands of federal agents at the ready, law enforcement has tried to plan for every contingency.
"It'd be a terrible day if we had to shoot down an airliner to defend folks on the ground, but that's the way it is and everyone's willing to accept that and prepared to do it," said Col. Dave Miles, an Air Force liaison for the Department of Homeland Security.
The coast guard has prepared for Obama's swearing-in -- and for the anticipated influx of 2-3 million people to the national capital -- with armed, fast-moving boats set to patrol the waters around the city. SWAT teams, too, are at the ready.
"We cannot let our guard down. We have to give it 100 percent. There is no room for mistakes," said Joseph Perssichini, Jr. of the FBI's Washington field office.
Authorities said potential threats range from Al Qaeda-inspired terrorists to solitary assailants who could attack without warning.
"You will see some of the police officers in every area of the city on horseback, motorcycles," said Cathy Lanier of the Metropolitan Police Department of the District of Columbia. "Just about every way you can imagine -- [there will be] lots and lots of foot beat officers."
The security goes beyond manpower and boots on the ground. Authorities are utilizing technology to keep the festivities safe. Precautions range from satellites and surveillance cameras aimed at the city to electronic sensors sniffing the air for signs of radiation and biological or chemical weapons.
"Whether it has to do with human resource asset, technology asset, there's no asset that we're not going to use to make this a safe event," said Secret Service director Mark Sullivan.