A roller coaster of emotions gripped politicians, pundits and the American public in Washington, D.C., today as the nation awestruck by the inauguration of the nation's first black president and jubilant about the celebrations to follow turned its concern to the collapse of Sen. Ted Kennedy this afternoon.
As the senator received medical care at a Washington hospital, black and white, young and old, stars and starstruck witnessed history Tuesday as Barack Obama waved to roaring crowds along the inaugural parade route after taking the oath of office to become the nation's 44th president.
Obama's swearing in as the first black president elicited a range of emotions from the throngs of onlookers who flocked to Washington today for the inauguration, the parade and balls that follow.
An estimated 1.8 million people in the nation's capital watched President Obama take the oath of office and deliver his hotly-anticipated inaugural address. As of late afternoon, two senior law enforcement officials said they did know of not a single arrest on the National Mall.
Watch live coverage of the Inauguration all day and go to the Inauguration Guide for all of ABC News' coverage details.
Before the swelling crowd, Obama emphasized that it will be up to people from all walks of life to help bring nations closer together.
"What is required of us now is a new era of responsibility -- a recognition, on the part of every American, that we have duties to ourselves, our nation, and the world, duties that we do not grudgingly accept but rather seize gladly, firm in the knowledge that there is nothing so satisfying to the spirit, so defining of our character, than giving our all to a difficult task," Obama said in his inaugural address.
"This is the price and the promise of citizenship."
Far outside the Beltway, others came together at homes, schools, work places and watch parties across the country and around the world to observe America's transition of power, some celebrating in places as distant as Obama's father's hometown of Kogelo, Kenya.
In the Middle East, television stations aired Obama's inauguration with one notable exception -- Iraq's state-run Iraqiya Television.
Even Pope Benedict sent Obama well wishes today via telegram.
"Under your leadership may the American people continue to find in their impressive religious and political heritage the spiritual values and ethical principles needed to cooperate in the building of a truly just and free society, marked by respect for the dignity, equality and rights of each of its members, especially the poor, the outcast and those who have no voice," the Pope wrote.
"Upon you and your family, and upon all the American people, I willingly invoke the Lord's blessings of joy and peace," he added.
"No triumph tainted by brutality could ever match the sweet victory of this hour and of what it means to those who marched and died to make it a reality," said California Sen. Dianne Feinstein just before the Obama took the oath of office. "Our work is not yet finished, but future generations will mark this morning as the turning point for real and necessary change in our nation."
People began gathering before dawn on the National Mall in Washington, D.C. By 7 a.m. crowds were packed in from the Capitol to the Washington Monument. Many walked for miles in the bitter cold, and others drove hundreds of miles.
By 9 a.m., nearly 410,000 people had ridden Washington's Metro train system, according to a Metro spokeswoman. The National Park Service also announced that due to the already overwhelming crowd size, it would close down a large portion of the National Mall. The National Park Service was instead redirecting people to the Washington Monument grounds.
Some recognizable names were among the sea of faces.
"We had to do a little walking, but it's nothing compared to many years, hundreds of years, that it took to get to this point in history for this country," director Spike Lee told ABC News' Robin Roberts.
"It's a lot of emotions really, because, I never thought it would happen either," said Magic Johnson.
"I am full of hope," said actor Denzel Washington. "You know, I feel that we can only go up from here. United. If we're all together, if we work together and respect our civic duty."
Just before Obama stepped up for the swearing in, pastor Rick Warren reflected on the moment in his invocation.
"We celebrate a hinge-point of history with the inauguration of our first African-American president of the United States," Warren said. "We are so grateful to live in this land, a land of unequaled possibility, where the son of an African immigrant can rise to the highest level of our leadership."
Pundits were quick to reflect on the president's words as soon as his speech was over.
"I think Obama was very careful in his speech today not to step forward and say, 'We're breaking with the past, we're starting everything fresh, here's how we're gonna do it,'" said Columbia University lecturer Joe Cutbirth. "I think it was much more sublime than that. I think he came out and said there are 44 people who have taken this oath and then he kind of talked, I felt like, as a continuation of the best part of our history. And it seemed to me like that was the frame for the speech."
"I think what he is saying to this country is, 'It's time to stand up and pull together and work," said Politico senior editor Beth Frerking. "That to me was the takeaway message of this speech."
During the Martin Luther King Jr. holiday weekend, more than 1 million people who traveled to the nation's capital and countless others who remained in their hometowns were similarly abuzz about the shift in Washington, D.C.
In the lead up to Inauguration Day, leaders in predominately black communities talked about their hopes for the future. Some recalled memories from decades ago when they attended Martin Luther King, Jr.'s March on Washington. Young students weighed in on how they'll overcome obstacles to realize their dreams.
"Oh my God, this is a dream," Nikki LeCompte told ABC News after driving from Houston to Washington. "I'm the generation after King, and my kids are the generation of Obama."
According to the latest poll numbers, three in four Americans were planning to watch or listen as the 44th president took office.
"That's all we want is one good president for all people," 107-year-old Ann Nixon Cooper told ABC News from her Atlanta home.
As the spotlight centered on him over the weekend, Obama threw it back to shine on the American people.
"What gives me the greatest hope of all is not the stone and marble that surrounds us today, but what fills the spaces in between," Obama told Sunday's crowd packed between the Lincoln Memorial and the Washington Monument for inauguration weekend's "We are One" concert.
"It is you -- Americans of every race and region and station who came here because you believe in what this country can be and because you want to help us get there."
"As I prepare to assume the presidency, yours are the voices I will take with me every day I walk into that Oval Office -- the voices of men and women who have different stories but hold common hopes; who ask only for what was promised us as Americans - that we might make of our lives what we will and see our children climb higher than we did," he said in his Sunday speech.
ABC News' Viviana Hurtado, Pierre Thomas, Gary Langer, Richard Coolidge, Jason Ryan, Ann Compton, Howard Schoenholtz, Chuck Lustig, Jonathan Newman and Zoe Magee contributed to this report.