Barack Obama stands at the precipice of history Tuesday morning, hours before he will shatter centuries-old racial barriers to be sworn in as America’s 44th president.

Crowds expected to approach two million began taking shape in the nation’s capital in the early morning hours, despite weather forecasts that call for bitter cold and possible snow.

People streamed into Washington, D.C., packing mass transit and suburban subway parking lots before dawn as out-of-towners and area residents alike headed for Pennsylvania Avenue and the National Mall for the swearing in ceremony.

A festive atmosphere surrounded the nation’s capital throughout the weekend as onlookers relished in the chance to witness history.

By 4 a.m. Tuesday, lines of riders formed in suburban parking lots for the Metro transit system, which opened early and put on extra trains for the expected rush. Many parking lots filled up and had to be closed.

Streets around the Capitol quickly filled with people, and security checkpoints were mobbed.

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, 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.

Mr. Obama’s ascendancy marks a milestone once unthinkable in a nation that has struggled with racial issues since its founding and where segregation was practiced in many Southern states decades ago. It takes place outside the U.S. Capitol, which slaves helped build. Mr. Obama will take his oath on the same Bible used at the 1861 inauguration of Abraham Lincoln, whose Emancipation Proclamation ended slavery.

Mr. Obama’s election electrified millions across the globe with the hope that the new America leader would be more inclusive and open to the needs of people and governments worldwide, more collaborative and more inclined to attack problems with diplomacy than with military power.

Tuesday’s ceremony is the culmination of a remarkable ascent for the 47-year-old Democrat, who moves into the Oval Office as the nation’s fourth youngest president. In less than five years, he rose from a little-known Illinois state lawmaker to the nation’s highest office, persuading Americans that despite his relative inexperience, he could turn around the economy, end the Iraq war and restore U.S. standing in the world.

A gifted, inspirational speaker, Mr. Obama has raised the hopes of millions as he outlined a new course for the United States. He has promised to emphasize diplomacy, seek global solutions to climate change, reject torture and shut down the Guantanamo Bay prison.

Mr. Obama’s presidency puts Democrats firmly in charge of Washington. They will control both chambers of Congress and the White House for the first time since 1994.

By custom, Mr. Obama and his wife, Michelle, were invited to the White House for coffee with Mr. Bush and his wife, Laura, followed by a shared ride in a heavily armored Cadillac limousine to the U.S. Capitol for the transfer of power.

Continuing a White House ritual, President George W. Bush left a note in the Oval Office for President-elect Barack Obama, wishing him well as he takes the reins of the executive branch.

Before noon, Mr. Obama steps forward on the West Front of the U.S. Capitol to take the oath of office from Supreme Court Chief Justice John Roberts. The 35-word declaration has been uttered by every president since George Washington.

(Source: CBS2 HD)