President Barack Obama took his ceremonial oath of office on Monday at the U.S. Capitol before an enormous crowd on the National Mall.
He was officially sworn in on Sunday in a private ceremony, marking the start of his second term.
Vice President Joe Biden also took his ceremonial oath on Monday.
WASHINGTON -- Crowds filled the National Mall on a crisp Monday for the second inauguration of President Barack Obama, who will recite the oath of office and address the nation a day after formally beginning his second term.
The nation's first African-American president will become only the 17th U.S. leader to deliver a second inaugural address before heading the traditional parade up Pennsylvania Avenue to the White House.
Amid the pomp and ceremony, with heralding trumpets announcing the arrival of dignitaries and red, white and blue bunting festooned throughout central Washington, the event symbolizes American democracy with a peaceful extension of power based on last November's election that returned Obama to the White House.
"Welcome to this celebration of our great democracy," Sen. Charles Schumer, D-New York, declared in opening the formalities of the nation's 57th presidential inauguration.
Two former presidents, Cabinet officials, Supreme Court justices, members of Congress and other dignitaries filled the temporary facade on the West Front of the U.S. Capitol.
Not in attendance was Veterans Affairs Secretary Eric Shinseki, the designated "survivor" for the event.
Satisfying the constitutional obligation to be sworn in on January 20, Obama and Vice President Joe Biden took quiet oaths the day before Monday's public ceremony at the Capitol.
Obama begins the second half of his presidency with the opportunity to make it more historic but facing some of the same challenges that he struggled with in the first four years.
He hosted congressional leaders from both parties for tea on Monday morning, and will take part in a traditional lunch with them after his inauguration speech.
On the Mall, Carlos Arieta and his wife, Sharon, took in the scene after driving from Atlanta to witness history. The former Washington residents said it was their first inauguration in person.
Surprised by the throngs gathered a few hours before the speech on a clear morning with temperatures just above freezing, Arieta said "it's nice to see all the different kinds of people."
A new CNN/ORC International poll released Monday indicated less excitement this time than four years ago, when nearly two million people crowded the Mall despite frigid weather for Obama's historic first inauguration.
In January 2009, nearly seven in 10 Americans questioned in a CNN survey said they were thrilled or happy that Obama was about to take office. Now, according to the new, that number is down 18 points, to 50%.
Back then, six in 10 saw Obama's inauguration as a celebration by all Americans of democracy in action, with just 39% saying it was a political celebration by the supporters of the winning candidate.
Now, the numbers are nearly reversed, with 62% saying the second inauguration is a celebration by those backing the president, and 35% saying it's a celebration of democracy.
"The thrill is gone, along with the hope that the start of a new presidential term of office will bring a divided nation together," said CNN Polling Director Keating Holland.
Monday's inaugural address will have a "hopeful" tone, Obama senior adviser David Plouffe told CNN, explaining that the president would "remind the country that our founding principles and values still can guide us in a changing and modern world."
Plouffe said that "the challenges and opportunities are enormous" in the president's second term, and that those challenges would be confronted as soon as the inaugural celebrations play out.
Reality of second-term presidencies
The smaller crowd this time around reflects the reality of second-term presidencies, when the novelty and expectations of a new leader have been replaced with the familiarity and experiences of the first act.
For Obama, that difference is even sharper. His historic ascendancy to the White House in 2008 came with soaring public hopes and expectations for a new kind of governance that would close the vast partisan gulf developed in recent decades.
However, a litany of challenges including an inherited economic recession and repeated battles with congressional Republicans over budgets and spending only hardened the opposing positions in Washington.
Obama's signature achievements, including major reforms of the health care industry and Wall Street, became symbols of political division, with opponents constantly accusing him of hindering needed economic recovery.
A second-term Obama has vowed to press for an overhaul of the nation's immigration policies and new ways to boost the sputtering economy, proposals that are bound to spark
And the shootings at a Connecticut elementary school last month put the divisive issue of gun control on his immediate agenda.
CNN polling released Sunday showed a majority of Americans -- 54% -- believe Obama will be an outstanding or above average president in his second term, while 43% said he'd be poor or below average.
And while overall, seven in 10 Americans hope the president's policies succeed, only four in 10 Republicans feel that way, with 52% hoping that Obama will fail.
Obama's swearing-in on Sunday took place in the ornate Blue Room, an oval-shaped reception space in the president's official residence, where he was joined by his wife, Michelle, and his two daughters.
The event took less than a minute and Obama didn't make any formal remarks or statements.
He did take a moment to hug his wife and daughters, exclaiming: "I did it!"
Justice Sonia Sotomayor performed the honors for Biden at his home at the Naval Observatory in Washington, where the vice president's extended family and a few Cabinet officials gathered to watch the ceremony.
Sunday evening, the Obamas watched Latino acts at "In Performance at the Kennedy Center," which was followed by the "Let Freedom Ring" concert. The "Red, White and Blue Inaugural Ball" and "Hip-Hop Inaugural Ball" closed out Sunday's activities.
Obama also thanked donors at an event at the National Building Museum, telling them, "When we put our shoulder to the wheel of history, it moves forward."
But Obama also told them that his remarks were going to be short, given the speech he would be delivering on Monday, saying, "There are a limited amount of good lines, and I don't want to use them all up."
CNN's Tom Cohen, Dana Davidsen, Ashley Killough, Paul Steinhauser, Dana Bash, Jessica Yellin, Dan Lothian, Brianna Keilar, Kevin Liptak and Gregory Wallace contributed to this report.