As security officials work overtime to get the nation’s capital ready for the biggest inaugural bash in U.S. history, they say that the most daunting challenge is preparing for the unexpected.

The U.S. Secret Service, which is steering the security plan with the involvement of Park Police, National Guardsmen and a humongous force of 57 federal and local agencies, is focusing on such issues as: bomb threats, civil disturbances, safe airspace, the likelihood of foreign terrorism and local loonies not too pleased with the thought of an African-American president in the Oval Office.

"We do not have a specific threat at this time," Joseph Persichini Jr., head of the FBI's Washington Field Office, told the Washington Post. He noted, however, that agents are on guard for anyone suspicious doing surveillance. But threats aren't limited to violence or terrorism.

“Freezing or rainy weather could send people fleeing for shelter or medical attention,” the Post points out. The D.C. Fire and Emergency Medical Services Department is among the many agencies across the region gearing up for demands.

"There's no question: The more people you have packed into a small location, the greater the threat and the greater potential of damage if something does happen," said Louis R. Mizell Jr., a counterterrorism consultant and author.

Adding to the security challenge is the fact that long after the official inaugural ceremony and parade are over, there will be at least 70 concerts, balls and other events in close proximity.

"You've gone from a one-day event to a four-day event," said Persichini Jr.