President Obama used his second inaugural address on Monday to urge Americans to unite behind him and act on climate change, immigration reform and gun control, leveraging newfound political capital ahead of contentious fights over a sweeping set of progressives policies

"This generation of Americans has been tested by crises that steeled our resolve and proved our resilience," Obama said from the west side of the Capitol just before noon on Monday. "A decade of war is now ending. An economic recovery has begun. America's possibilities are limitless, for we possess all the qualities that this world without boundaries demands."

Obama called for bipartisanship, citing public frustration with gridlock in Washington. Yet, his address before hundreds of thousands of supporters served as a reminder of the liberal vision on which Obama campaigned.

"We, the people, understand that our country cannot succeed when a shrinking few do very well and a growing many barely make it," Obama said, reflecting the populist tone that has become more commonplace in his speeches.

Hundreds of thousands of people lined the National Mall to watch the nation's first black president kick off his second term. Obama was officially sworn into office in a private ceremony at the White House Monday, meeting the constitutional mandate to begin his second term on Jan. 20.

Obama mostly spoke only generally, saving policy specifics for his State of the Union address next month. However, he alluded to immigration, gun control and even a few policy proposals, such as climate change, which he steered clear of in his first term.

"Our journey is not complete until we find a better way to welcome the striving, hopeful immigrants who still see America as a land of opportunity; until bright young students and engineers are enlisted in our workforce rather than expelled from our country," he said. "Our journey is not complete until all our children, from the streets of Detroit to the hills of Appalachia to the quiet lanes of Newtown, know that they are cared for, and cherished, and always safe from harm."

Obama also made a strong push for climate-change legislation, pleasing his liberal base, which accused him of ignoring the issue during his first term.

"We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations," he said. "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."

That line brought sustained applause in the crowd on a blustery day on Capitol Hill -- though not nearly as cold as the president's last inaugural.

"Amen," said Chris Sanchez, who made the trip from New York City and had been waiting since 7 a.m. to hear the president. "I've been wanting him to talk about global warming for four years."

The president has a heavy schedule of inaugural events Monday, including lunch with lawmakers, a parade and inaugural balls.