WASHINGTON (AP) -- Barack Obama launched his second term as U.S. president by confronting conservative opponents in Congress, declaring in an inaugural address before nearly a million spectators that he will tackle climate change, protect America's social safety net and pursue other decidedly liberal goals.
The president -- often criticized by supporters for being too quick to compromise in his first term only to get little in return from Republicans -- spoke with fire for the center-left political agenda that first carried him into the White House four years ago.
He defended spending on social programs for the poor, the ailing and the elderly. He promoted immigration reform and gay marriage. And he unexpectedly gave one of his most impassioned calls for action on climate change, an issue that has not been at the forefront of the political debate.
The first African-American president starts his second term emboldened by a decisive re-election victory, an improving -- though still weak -- economy and the winding down of a decade of wars. But he faces a political landscape as divided as before: Republicans control the House of Representatives and his fellow Democrats run the Senate.
Obama tried to make clear that he will not stand for the partisan fighting that often marked his first term, thwarting his efforts to pass aggressive plans for jobs creation and deficit reduction. Without mentioning Republicans or Democrats, he demanded moderation from those whose refusal to compromise twice brought the nation to the brink of fiscal crisis.
"We cannot mistake absolutism for principle, or substitute spectacle for politics, or treat name-calling as reasoned debate," Obama said, "We must act, knowing that our work will be imperfect. We must act, knowing that today's victories will be only partial."
It was an acknowledgement that not only Republicans, but also the president and his Democratic Party must compromise. Yet the speech was a far cry from the more conciliatory tone he tried to set in his first inaugural address four years ago.
Then a lightly experienced first-term senator, Obama entered the presidency vowing to stem the partisan anger that engulfed the country. He appeared to be taken aback by the ferocity of Republican resistance, which gave birth to the conservative tea party movement in 2009. The limited government, anti-tax conservatives forced him to pass his health care overhaul without a single Republican vote, and fueled huge Democratic setbacks in the 2010 congressional elections.
Obama's decisive win in November and Republican setbacks in Congress chastened the opposition a bit, but Republicans still adamantly oppose the president's call for increased taxes on the wealthy and investing more on infrastructure and education. That poses the central challenge to his hopes for an ambitious second-term agenda.
The Republican opposition wants to target spending cuts on the federal Medicare health care program for elderly Americans and other programs to slow the rise in a $16.4 trillion national debt.
Obama defended such programs with an overt jab at the Republican presidential candidate he defeated, Mitt Romney, who during the campaign criticized the 47 percent of American voters "who are dependent upon government, who believe that they are victims." Romney's running, Congressman Paul Ryan, declared during the campaign that the U.S. was a welfare state creating more "takers" than "makers."
Programs like Medicare, Obama said, "do not make us a nation of takers; They free us to take the risks that make this country great."
"Our country cannot succeed when a shrinking few do very well and a growing many barely make it," Obama said outside the Capitol, looking out at the crowd of people jammed shoulder to shoulder on the National Mall.
His demand for action on climate change also flipped around an accusation that some Republicans leveled at him during the campaign: That his administration was weakening the country by trying to lead the world "from behind."
"The path towards sustainable energy sources will be long and sometimes difficult. But America cannot resist this transition; we must lead it," Obama said. "We cannot cede to other nations the technology that will power new jobs and new industries - we must claim its promise."
He offered an impatient warning for global warming doubters. "Some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires, and crippling drought, and more powerful storms," he said.
Obama also cited a need for immigration reform and gun-control legislation. Both efforts will bring bitter partisan wrangling, especially the gun debate in the raw aftermath of last month's Connecticut school shooting that left 20 young children and six educators dead.
Obama marked a new direction in foreign policy as the U.S. prepares to pull troops from Afghanistan, ending the country's longest war. He challenged those who favor aggressive