President Obama had mentioned climate change in prominent speeches before Monday.

In his November victory speech, he spoke of protecting America’s children from “the destructive power of a warming planet.” At his first inauguration, he promised to “harness the sun and the winds and the soil to fuel our cars and run our factories.”

But in his remarks Monday after taking the oath of office, Obama chose to make a moral case — rather than an economic or national security one — for taking action. “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.

The decision to frame a response to global warming as a defining aspect of his legacy has encouraged his environmental allies and reignited concerns among congressional Republicans and industry opponents. And it signaled that the issue continues to weigh on Obama, even as he and his aides have placed budget negotiations, immigration and gun control higher on their agenda.

“It was about climate change for climate change’s sake, and for his legacy,” said Margie Alt, Environment America’s executive director. “This was more powerful than anything I remember him saying. It was a moral mandate that he laid out.”

President Obama delivers remarks at the 57th presidential inauguration on Monday. (The Washington Post)

Obama made a point of highlighting how much emphasis he gave the issue after Rep. Henry A. Waxman (D-Calif.) thanked him afterward for mentioning climate change.

“I didn’t just mention it, I talked about it,” Obama parried, according to Waxman.

In interviews this week, administration officials and those who lobby on both sides of the issue said Obama and his aides are examining the same regulatory options they had been considering before the election. Those include a possible cap on greenhouse gas emissions from existing power plants, policies to promote energy efficiency in the public and private sectors, ways to promote combined heat and power generation at industrial facilities, and an expansion of biofuel use and other forms of renewable energy at the Pentagon.

“I think he has a lot of tools, and they’re evaluating how to use them,” said Carol Browner, who served as assistant to the president on energy and climate change during Obama’s first two years and is now a distinguished senior fellow at the Center for American Progress.

The White House is likely to build a public effort to rally support for these initiatives through the group Organizing for Action, the offshoot of Obama’s reelection campaign. Its executive director, Jon Carson, served as the White House’s liaison to environmental groups during the president’s first term.

“Having Jon over there gives me confidence,” Alt said. “They will need to do a lot of work to set themselves — and the administration and the country — up to do this. It’s not going to be easy.”

Still, several experts questioned whether the Environmental Protection Agency — which oversees the effort to impose carbon limits on existing coal- and gas-fired utilities — would be able to assemble the rules before the end of the year.

Ross Eisenberg, vice president for energy and resources policy at the National Association of Manufacturers, said Obama’s inaugural remarks would embolden administration efforts to address climate change “through the existing environmental laws.” But he added, “Despite the rhetoric yesterday, really, how quickly will they move?”

And Rep. Ed Whitfield (R-Ky.), who chairs the House Energy and Commerce subcommittee on energy and power, said his party will continue to resist administration efforts to mandate limits on carbon emissions.

“Whether it be cap-and-trade, a carbon tax, or new greenhouse gas regulations, House Republicans will continue to oppose any plan that drives up energy costs and puts American businesses at a competitive disadvantage,” Whitfield said in a statement.

White House spokesman Jay Carney made it clear to reporters Tuesday that “bipartisan opposition to legislative action is still a reality,” emphasizing that the administration continues to view its climate policy as a way of achieving other goals, such as the expansion of renewable energy.

“Climate change is not — you don’t pursue action that helps deal with that problem just because of the problem itself, but because there are huge opportunities in alternative energy,” Carney said.

League of Conservation Voters President Gene Karpinski said that of all the issues facing the White House, climate change “may be the hardest one to legislate. But here you can make huge changes without legislation.”

In some cases, the White House will have to grapple with climate questions that may force difficult economic decisions. On Tuesday, Nebraska Gov. Dave Heineman (R) approved a revised route through his state for the Keystone XL pipeline, which will transport heavy crude oil from Alberta’s oil sands to Gulf Coast refineries.

In a briefing with reporters Tuesday, Senate Environment and Public Works Committee Chairman Barbara Boxer (D-Calif.) said that approving Keystone “would undo any good that was done by the increase in fuel economy” that the administration accomplished in its first term, because extracting the oil releases significant amounts of carbon.

The pipeline has become such a lightning rod in the environmental community that on Tuesday, the Sierra Club’s board of directors approved the use of civil disobedience for the first time in its 120-year history in an effort to oppose it.

And Waxman, as he chatted with Obama at the inaugural lunch at the Capitol on Monday, made it clear that even a lengthy passage in a high-profile speech was not enough to secure the president’s legacy on climate.

“We’ve got to do more than talk about it — we’ve got to act,” the veteran legislator said.

“You’re right,” Obama said, before moving on to the next guest.