WASHINGTON -- Barack Hussein Obama launched his second term as the nation's 44th president Monday, urging an increasingly divided nation to move past polarizing debates and live up to its founding ideals by uniting to solve the country's problems."America's possibilities are limitless, for we possess all the qualities that this world without boundaries demands: youth and drive, diversity and openness, an endless capacity for risk and a gift for reinvention," he said on a crisp, sun-filled afternoon. "My fellow Americans, we are made for this moment, and we will seize it, so long as we seize it together."His 18-minute inaugural address, delivered in front of hundreds of thousands of people and televised to millions across the globe, offered a clear agenda for his second term, marshaling the federal government to protect the rights of gays and lesbians, combat climate change, provide opportunities for illegal immigrants, and help the downtrodden and middle class get a better foothold in a changing and still fragile economy.A sea of spectators packed the National Mall to watch Obama, 51, sworn in to office just before noon on the west side of the U.S. Capitol, the first Democrat in seven decades to twice win a majority of the popular vote. First lady Michelle Obama and daughters, Sasha, 11, and Malia, 14, looked on, as did former Democratic Presidents Jimmy Carter and Bill Clinton. The two living Republican former presidents didn't attend, the ailing George H.W. Bush and son George W. Bush."O-bam-a!" the crowd chanted. "O-bam-a!"Noticeably grayer than when he first took office, Obama officially started his second term 24 hours earlier, after a brief private ceremony at the White House. Monday's proceedings followed the tradition of delaying the public inauguration a day when the official date prescribed by the Constitution falls on a Sunday.The nation's 57th inauguration comprised five days of patriotic parades and fancy balls, solemn prayers and many receptions for donors and supporters. It was capped by dances with the first lady at two inaugural balls Monday night."At what place would you want to be on Inauguration Day?" asked Camille Page of Corona, Calif. "This is a once-in-a-lifetime experience. ... I will be proud to tell my grandchildren about it."Monday's events were jubilant, though they didn't have the same excitement as four years ago, when a young senator promising hope and change became the nation's first black president. Officials estimated that as many as 1 million people turned out, far short of the nearly 2 million in 2009 but an above-average audience for a second-term inauguration.The crowds led to a maze of street closures, clogged subways, heightened security and the National Mall filled with 1,500 portable toilets, five large-screen TVs and 6,000 members of the National Guard in town helping with crowd control.After a bitter election and constant clashes on Capitol Hill, Obama used his inaugural address to encourage those with differing views to work together to accomplish something, even if it's not everything."For now decisions are upon us, and we cannot afford delay," he said. "We cannot mistake absolutism for principle, or substitute spectacle for politics, or treat name-calling as reasoned debate. We must act; we must act knowing that our work will be imperfect."In his second term, Obama faces a polarized political climate.He must address fiscal issues -- tax revisions and spending cuts -- and pressing international obligations: stopping Iran's nuclear program, navigating an end to the war in Afghanistan and avoiding tensions with China over the administration's "pivot" to Asia. In the weeks since he defeated Republican Mitt Romney, he has battled with Republicans in Congress over tax increases and spending reductions.Outlining the nation he envisions, he sounded the themes of his recent campaign as a call for using the federal government to shift the benefits of the country and its economy to the poor and middle class and away from the wealthy."We, the people, understand that our country cannot succeed when a shrinking few do very well and a growing many barely make it," he said. "We believe that America's prosperity must rest upon the broad shoulders of a rising middle class."He linked past sacrifices to current struggles for equality for all: economic equality for the poor, civil rights for gays, equal pay for women."We, the people, declare today that the most evident of truths -- that all of us are created equal -- is the star that guides us still," Obama said. "Just as it guided all those men and women, sung and unsung, who left footprints along this great Mall, to hear a preacher say that we cannot walk alone; to hear a King proclaim that our individual freedom is inextricably bound to the freedom of every soul on Earth."Republicans, who joined Obama at the White House early for coffee and later at the Capitol for lunch, expressed hope that both sides can work together on fiscal issues."The president's second term represents a fresh start when it comes to dealing with the great challenges of our day," said Senate Minority Leader Mitch McConnell, R-Ky.