Four years ago, a grave President Obama looked out over the Mall and warned of costly wars, economic peril, pervasive greed and the nation’s “collective failure to make hard choices.”

On Monday, nearly three months after American voters chose him again, a brusque Obama directed his warning toward a Republican Party he once believed he could win over. In outlining a liberal last-term agenda, Obama made clear that he still intends to change the country — but now without first changing Washington.

“Progress does not compel us to settle centuries-long debates about the role of government for all time, but it does require us to act in our time,” Obama told the crowd stretching before him from the Capitol. “For now decisions are upon us and we cannot afford delay.”

Obama’s second inaugural address served as an epilogue to his first, which was defined by its surprisingly stern tone. The occasion then was the historic swearing-in of the nation’s first African American president, but Obama chose instead to prod what he called a country “in the midst of crisis.”

With more than 150,000 U.S troops fighting two wars and a teetering financial system, Obama urged his audience to “pick ourselves up, dust ourselves off, and begin again the work of remaking America.” He said setting aside partisanship and other “childish things” would be part of a national rehabilitation.

On Monday — with one war over, another ending and the economy slowly growing — Obama echoed some of the same broad themes, including the need for the nation’s political leaders to act in common cause to prepare the country for a rapidly changing world.

But he did so with more partisanship and populism than he did on a far colder day four years ago. The more optimistic tone and specific ambition of the speech reflected not only the country’s halting progress over that time, but also his own evolution as a political leader in a divided country.

“What I was struck by was how much more committed to an agenda he seems to be than he was in the last inaugural,” said Robert Dallek, a presidential historian who attended a dinner with Obama at the White House earlier this month to talk about second-term strategies. “Now he’s going to push what he believes in.”

Indeed, the caveats and compromises that Obama included in his first inaugural to appease leery Republicans were almost entirely absent from the arguments he made this time. He offered instead a list of liberal solutions that he intends to pursue, part of what one senior adviser described as “a project of advocacy on behalf of the middle class.”

As Obama said pointedly: “For we, the people, understand that our country cannot succeed when a shrinking few do very well and a growing many barely make it.”

Speaking on the national holiday celebrating the life of Martin Luther King Jr., Obama also invoked the civil rights movement as the rationale for his priorities throughout the 181 / 2-minute address, arguing that climate change, immigration reform, gun control, and equality for gay men and women represent the civil rights concerns of his generation.

In one rhetorically stirring moment, Obama cited the seminal gay-rights demonstrations that broke out after police raids on New York City’s Stonewall Inn more than four decades ago, listing it alongside the bloody civil rights clash in Selma, Ala., and the start of the women’s suffrage movement in Seneca Falls, N.Y.

For a politician who endorsed same-sex marriage only last year, Obama went further than any of his predecessors in making gay rights a central part of his push for economic and social equality.

Obama also pledged to protect entitlements from budget cuts and defend the vulnerable from a warming climate and gun violence in what amounted to a thematic preview of next month’s State of the Union address, which he will use to more fully detail his plans and approach.

Health-care programs for the elderly and the poor “do not make us a nation of takers,” Obama said, borrowing the pointed language used by GOP opponents in the last campaign.

“They free us to take risks that make this country great,” he said to applause.

Obama’s first address is a way to measure what he has managed to achieve and where he has fallen short. “Our time of standing pat, of protecting narrow interests and putting off unpleasant decisions — that time has surely passed,” Obama said in 2009.

In the epilogue delivered Monday, Obama effectively accepted Washington’s enduring partisanship, something he once pledged to end. But he also warned that he would demand action on an agenda that few Republicans have been prepared to support.

He used the phrase “We, the people” — the opening words of the Constitution’s preamble — at least five times to make the case that the country agrees with his views of where the country should be heading.

“What the speech said to me was that a new kind of liberal government is back,” said Sean Wilentz, an American history professor at Princeton University, describing it as an extension of the limited activism that Bill Clinton began.

“It’s not that you are going to evade politics or change politics or fix politics,” Wilentz said. “You are going to change the country by being political.”

Obama was less specific about how he intends to reengage the world after more than a year preoccupied with his own reelection.

He told the audience that “a decade of war is now ending,” as he maps out a schedule to bring the last U.S. troops home from Afghanistan by the end of next year. He also made clear that he would not be rushed into another war, tacitly referring to a confrontation with Iran over its uranium-enrichment program.

Beyond the specifics of his agenda, there is a message that Obama, the former Harvard law student and community organizer, wants to leave with an increasingly skeptical American electorate before he leaves office. He began that lecture Monday, invoking the civil rights movement again to declare that “our journey is not complete until no citizen is forced to wait for hours to exercise the right to vote.”

Citing the “unalienable rights” outlined in the Declaration of Independence, Obama said, “For history tells us that while these truths may be self-evident, they’ve never been self-executing.”

“That while freedom is a gift from God,” he continued, “it must be secured by His people here on Earth.”

His senior advisers say he will continue to talk about the value of civic engagement — in the service of his agenda and beyond — as a way to change the country throughout his last term.

“It is something that holds great meaning to him,” said one senior adviser, who requested anonymity to describe Obama’s plans. “He’s an organizer.”