Obama's Challenge: Worst Economic Crisis in 70 Years

Barack Obama prepared to make history Tuesday as the first black U.S. president, riding a wave of public optimism he will need to tap to deal with the worst economic crisis in 70 years and two wars.

Hundreds of thousands of people, bundled up against the cold, packed Washington's Mall, which stretches 2 miles from the Capitol to the Lincoln Memorial on the Potomac River and along Pennsylvania Avenue to the White House.

There was late word that U.S. authorities were investigating a potential threat, which they said was of uncertain credibility, in connection with the inauguration, the U.S. Homeland Security Department said on Tuesday.

Television pictures showed a sea of people, many waving American flags, in the grassy plain of the Mall about two hours before Obama, a Democrat, was due to be sworn in as the 44th U.S. president just before noon EST, taking over from Republican George W. Bush