President Obama confronted Republicans on the science of climate change in a sometimes barbed State of the Union address that described rising temperatures as the greatest threat to future Americans.

The speech collided with the promises of newly empowered Republicans in Congress to depict Obama’s climate and energy policies as symbols of excessive liberalism before the presidential elections next year. Obama was still delivering his address when a senior Republican senator described his climate views as part of a “socialist agenda.”

Speaking on the heels of new research showing that 2014 was the warmest year on record, Obama warned that the impacts of greenhouse gas emissions could worsen weather, erode the economy and endanger children’s health.

“Now, one year doesn’t make a trend, but this does: 14 of the 15 warmest years on record have all fallen in the first 15 years of this century,” Obama said.

“I’ve heard some folks try to dodge the evidence by saying they’re not scientists, that we don’t have enough information to act,” he added, referring to some Republicans who have made such statements. They include Ohio Rep. John Boehner, speaker of the House, who was sitting right behind him.

“The best scientists in the world are all telling us that our activities are changing the climate, and if we do not act forcefully, we’ll continue to see rising oceans; longer, hotter heat waves; dangerous droughts and floods; and massive disruptions that can trigger greater migration, conflict and hunger around the globe,” Obama added.

Some observers anticipated that the president would try to build public support for his Clean Power Plan, which U.S. EPA is developing to curb greenhouse gas emissions at new and existing power plants. But that appeal to the public never came. Obama instead issued a veiled warning to Republicans that their efforts to obstruct the upcoming rules and other climate programs could be portrayed as being harmful to children.

“I will not let this Congress endanger the health of our children by turning back the clock on our efforts,” Obama said.

The president’s sometimes defiant speech was delivered hours after a Senate debate on the other side of the Capitol struck similar themes. The Senate easily passed a modest energy efficiency amendment to a bill that’s meant to force Obama to either approve the Canadian Keystone XL pipeline or veto it.

Sen. Rob Portman (R-Ohio), whose name headlines the efficiency bill, described the development as “fantastic.”

Republicans might consider either outcome—Keystone XL approval or a veto—a victory as they seek to portray Obama, and Democrats, as favoring environmental issues over jobs. That narrative promises to help shape the presidential elections next year.

“President Obama will soon have a decision to make: Will he sign the bill, or block good American jobs?” said Sen. Joni Ernst (R-Iowa) of the pipeline legislation in her party’s rebuttal to the president’s speech.

Calling climate a ‘major vulnerability’ for the GOP

Obama mostly steered clear of Keystone XL, which he says will only be approved if it doesn’t exacerbate climate change by significantly expanding production in the Canadian oil sands. Instead, he urged Congress to address infrastructure programs nationally.

“So let’s set our sights higher than a single oil pipeline,” Obama said. “Let’s pass a bipartisan infrastructure plan that could create more than 30 times as many jobs per year and make this country stronger for decades to come.”

Before the speech, Bob Perciasepe, a former EPA official who is now president of the Center for Climate and Energy Solutions, said it would be beneficial if the president used his address to correct inaccuracies about EPA’s carbon rules for power plants. Opponents wrongly describe them as economically detrimental and bureaucratically rigid, Perciasepe said.

“All of these can be dispelled or at least modulated by the president laying out his views and the fact that he’s trying to provide a lot of flexibility for the states to be creative and find innovative approaches,” he added.

Perciasepe applauded Obama after the speech for highlighting the threat of climate change to a national audience. The president, however, did not explicitly mention the EPA carbon rules.

Others saw streaks of bravado in a president who might feel more confident about the political advantages of pressing for climate action. Paul Bledsoe, a senior fellow with the German Marshall Fund and a former Democratic adviser, said “the White House now sees the climate issue as a major vulnerability for the Republicans, especially for 2016.”

“By identifying climate change as the most critical issue for coming generations, the President is calling out not just science denial, but Republican attempts to undermine his specific domestic and international climate policies,” Bledsoe said in an email after the speech.

Veto threats loom

The speech comes amid a flurry of veto threats by the White House this month alone on legislative attempts to, among other things, approve the Keystone XL pipeline. The administration released two of those threats hours before the president delivered his address, including one that would kill a bill to grant automatic approval of natural gas pipelines if the Federal Energy Regulatory Commission fails to act quickly enough.

Republicans often seem comfortable shrugging off the climate issue, noting that GOP candidates cruised to victory in the midterm elections last year despite heavy spending by outside groups like Tom Steyer’s NextGen Climate, which depicted some GOP candidates as “deniers.” Ernst, who has questioned whether humans are contributing to higher temperatures, was one of those targeted by Steyer.

Sen. James Inhofe (R-Okla.), chairman of the Environment and Public Works Committee, described Obama’s climate policies as the hallmarks of a socialist agenda. He also said that EPA’s carbon rules due to be completed this summer are a “wealth redistribution scheme.”

“This is the real climate agenda the president chose not to address tonight,” Inhofe said in a video. “It is no wonder, because it would impose the largest tax increase in the history of America.”

Others say that Obama’s speech marked an important firewall against legislative efforts to roll back everything from EPA’s upcoming climate rules to future regulations to reduce methane emissions in the natural gas sector.

“There’s going to be a battle over this in Congress,” said David Goldston, director of governmental affairs at the Natural Resources Defense Council. “It’s important that that battle be teed up and the president make clear what’s at stake and that he’s going to see this through to the finish.”

Paris on the horizon

Though the focus was on domestic squabbles, a broader issue was evident in the president’s remarks: the role that the United States will play in international climate negotiations late this year in Paris.

Alden Meyer, director of strategy and policy for the Union of Concerned Scientists, said the president is fulfilling the demands of his political opponents by engaging with China and India on climate agreements.

“In a funny way, the opponents of action have laid the groundwork for the president tonight by hammering it in that it’s important to get other countries like China, India and Brazil on board,” Meyer said. “That has set him up to say, ‘Look, it’s working. I have engaged China, and I’m going to India next week.’”

Sen. Joe Manchin (D-W.Va.), said that Obama is requiring his state, and others dependent on fossil fuel economies, to shoulder the load of reducing emissions.

“We have a difference. We really do,” he said of Obama’s climate strategy. “I think I would like hear him acknowledging it’s a global problem. They call it a global climate, not a North American climate. It takes a global fix.”

Obama’s speech was wide-ranging, touching on a list of domestic and international priorities, including on combating terrorism. But Obama made it clear that some of his deepest concerns stem from the emissions of energy production and transportation.

“And no challenge—no challenge—poses a greater threat to future generations than climate change,” he said.