2/13/13: This story has been updated to include a statement by Florida Sen. Marco Rubio.
WASHINGTON—In President Obama's State of the Union speech  on Tuesday night, the theme of confronting climate change played more a supporting than a starring role.
Obama urged Congress "to believe in the overwhelming judgment of science—and to act before it's too late."
And he said that if a recalcitrant and divided Congress "won't act soon to protect future generations, I will. I will direct my Cabinet to come up with executive actions we can take, now and in the future, to reduce pollution, prepare our communities for the consequences of climate change, and speed the transition to more sustainable sources of energy."
But the president made no explicit promise to environmental advocates who had been hoping, since his soaring words on climate at his inauguration, that he would pledge to regulate carbon dioxide emissions that spew from existing power plants, or perhaps block the Keystone XL pipeline they so abhor .
Instead, the speech was another inflection point along the curve of his presidency: an assertion of his willingness to bypass Congress on big issues, but also a reminder that he must juggle competing priorities, including jobs, guns, immigration, health care, spending, taxes and global affairs.
In trimming his rhetorical sails, the president was navigating through treacherous political crosswinds—including fierce opposition to his agenda from Congressional Republicans, and equally adamant demands from a green movement marching on Washington this weekend to protest the Keystone XL pipeline.
In discussing energy, he emphasized security of supply and the creation of jobs as much as the pure green goals of cutting emissions. And he promised to continue cutting red tape and speeding up new gas and oil permits as "part of an all of the above plan."
On balance, many who follow climate issues closely said they were satisfied.
"I have the sense that he understands that he might be, and quite likely is, the last president who can keep us from going off the climate cliff," Becker said.
But organizers of Sunday's Keystone pipeline protest were less enthusiastic.
On Twitter, Bill McKibben , whose 350.org group  is helping to organize the march, wrote: "I'm interested in what the president says. I'm more interested in what the climate movement can push/free him to do."
For days, the capital had buzzed with rumors that the president might explicitly declare that he would control the carbon dioxide emissions of existing electric plants that burn fossil fuels, using a provision of the Clean Air Act that had lain untouched for so long that one Washington wag calls it "the 40-year-old virgin." At stake is some 40 percent of all the nation's emissions, especially from the burning of coal.
Although he didn't mention power plant emissions, many expect that such a regulation is on the way. Its advocates were quick to connect the dots.
Frances Beinecke , president of the Natural Resources Defense Council , issued a statement saying that the Clean Air Act already allows Obama to crack down on emissions "from our dirtiest power plants, the single greatest threat to our climate future. That will take presidential leadership. Americans are counting on it—and that's what the president delivered tonight."
The most specific proposals the president offered were of the kind that are easy to announce, and just as easy to forget. He proposed using some oil and gas revenues "to fund an Energy Security Trust that will drive new research and technology to shift our cars and trucks off oil for good." He also called for federal assistance to states with the best ideas for reducing energy waste in homes and businesses.
Obama can already claim to have made progress in curbing emissions through a combination of policy, market upheaval and serendipity: regulations, incentives, recession, and the natural gas drilling revolution.
"Last year, wind energy added nearly half of all new power capacity in America," he said. "So let's generate even more. Solar energy gets cheaper by the year – so let's drive costs down even further."
According to the Business Council for Sustainable Energy , renewable energy installations hit an all time high last year, natural gas equaled coal as a fuel for generating electricity, energy efficiency continued to improve, and emissions from the energy sector were headed toward their lowest level since 1994.
The Clean Air Act is the president's handiest tool for moving forward. The Natural Resources Defense Council has outlined  an approach, using that law, which it figures could cut the emissions from existing power plants by 26 percent from their peak in 2005.
The World Resources Institute has recommended  several other actions, all within the president's unilateral powers: phasing out the use of certain hydrofluorocarbons; setting lower standards for the methane emissions from natural gas systems; and focusing on more energy efficiency from homes, businesses and factories.
Obama set a new energy efficiency goal in his speech, but offered few specifics. "Let's cut in half the energy wasted by our homes and businesses over the next 20 years," he said. "We'll work with the states to do it. The states with the best ideas to create jobs and lower energy bills by constructing more efficient buildings will receive federal support to help make it happen."
Some executive actions should be easy to accomplish, and doing so quickly could make a difference right away. For example, now that Congress has extended the tax subsidy for wind energy projects, Treasury and the I.R.S. could quickly publish the fine print to make clear what it takes to qualify this year. Thirty members of the Sustainable Energy and Environment Coalition in the House have written  that without a quick clarification, uncertainty will continue to impede some wind projects.
None of this will come without a fight, as the president's harshest critics made plain.
"President Obama seemed more concerned about climate change than job creation," said Thomas Pyle , president of the Institute for Energy Research , a nonprofit that promotes free-market energy and environmental policy. "For this administration, a deadly hurricane means a chance for carbon taxes. A crop-killing heat wave means another opportunity to attack the coal industry."
In the official Republican respponse, Florida Sen. Marco Rubio stressed the importance of fossil fuels. "God also blessed America with abundant coal, oil and natural gas," he said. "Instead of wasting more taxpayer money on so-called 'clean energy' companies like Solyndra, let's open up more federal lands for safe and responsible exploration."
House Speaker John Boehner also weighed in with a detailed rebuttal of the president's climate remarks.  "The Obama administration's so-called 'green energy' agenda has destroyed jobs at home, shipped jobs overseas and left American taxpayers holding the bag for millions of dollars in failed pet projects," Boehner said.
The president is not without allies; but their path remains unclear.
Rep. Henry Waxman (D-Ca.) and Sen. Sheldon Whitehouse (D-RI) , both crusaders for action on climate, are putting together what they call a "bicameral climate change task force " to solicit ideas from a wide range of actors. And six scientific societies are calling on the president to convene a climate summit .
Senators Barbara Boxer of California and Bernie Sanders of Vermont, meanwhile, said they would unveil comprehensive legislation on Thursday that would impose a fee on carbon emissions to pay for much higher spending on conservation and renewable energy.
Despite the costs, not all business groups are opposed.
The Business Council for Sustainable Energy, which represents energy efficiency, renewable energy and natural gas companies, said that even if Congress remains gridlocked "in the short term, clean energy industries will work with the Administration to ensure that commercially-available clean energy technologies are fully utilized to reduce emissions."
One trick will be the administration's embrace of natural gas and oil drilling on public lands, part of its all of the above approach to transforming the nation's energy landscape.
"The natural gas boom has led to cleaner power and greater energy independence," Obama said. "That's why my administration will keep cutting red tape and speeding up new oil and gas permits."
In quick reply, the 350.org group dismissed that approach in a Twitter message: "Let's be clear: gas drilling is NOT a climate solution."