The email arrived at lunchtime Tuesday from a top aide to Environmental Protection Agency Administrator Scott Pruitt. “Our Big Day Today” read the subject line of the message, which went to thousands of EPA employees.

It detailed how President Trump would be visiting the agency, whose budget he recently proposed cutting by nearly a third, to sign a sweeping executive order aimed at unraveling efforts by President Barack Obama's administration to combat climate change.

“This is an important moment for EPA,” chief of staff Ryan Jackson wrote. “As the Administrator has mentioned many times, we do not have to choose between environmental protection and economic development.”

Jackson cautioned that there was “limited space” to see Trump sign his order in the EPA’s wood-paneled Map Room. But there was also limited interest from many of the agency’s career employees.

At the EPA, scientists are encountering renewed skepticism of their work, many employees have seen their offices slated for elimination altogether, and regulators are facing the prospect of dismantling environmental rules many of them spent years creating. Trump’s visit to headquarters Tuesday was met with frustration, resignation and varying levels of angst.

“What an insult,” said one longtime employee, who like others spoke on the condition of anonymity for fear of retribution.

“Needless to say, morale is at rock bottom,” said another, who noted that some employees had worn buttons that read “scientific integrity” in quiet protest.

But elsewhere in the building, the president and members of his Cabinet joined in celebrating a shift in policy direction with representatives from several energy industries that had been on the losing end of the previous administration’s policies.

Trump showed up at 2 p.m. as scheduled, surrounded by coal miners and coal executives, as well as Pruitt, Energy Secretary Rick Perry, Interior Secretary Ryan Zinke and Vice President Pence.

"Today, we're taking a great step in breaking the restraints that have become burdens," said Perry.

“We’re not going to allow regulations here at the EPA to pick winners and losers,” Pruitt promised.

The president, who devoted much of his remarks to praising coal miners, pipelines and U.S. manufacturing, declared, “We’re ending the theft of American prosperity and rebuilding our beloved country.”

The far-reaching order he unveiled Tuesday instructs federal regulators to rewrite key Obama-era rules curbing U.S. carbon emissions — namely the Clean Power Plan, which was intended to reduce greenhouse gas emissions from the nation’s electric plants. It also seeks to lift a moratorium on federal coal leasing and remove the requirement that federal officials consider the impact of climate change when making decisions.

In sum, it amounts to a wholesale rebuke of Obama's environmental efforts.

Several of the measures could take years to implement and are unlikely to change broader economic trends that are pushing the nation toward cleaner sources of energy than coal. But the order sent an unmistakable message about the direction in which Trump wants to take the country — toward unfettered oil and gas production, with an apathetic eye to worries over global warming.

Reactions to the new order came swiftly.

The Independent Petroleum Association of America's president and chief executive, Barry Russell, who was at the event, said in a statement that his group welcomed Trump's "bold decision to tackle the growing regulatory state and identify rules that harm the economy and threaten American jobs."

National Rural Electric Cooperative Association chief executive Jim Matheson, who also attended and whose group challenged the Clean Power Plan in federal court, said in an interview that he does not anticipate that many of his members will start building new coal-fired plants. But for those who already have invested heavily in keeping their coal plants operating, he said, “It has given them much greater flexibility to maintain more reasonably priced and affordable power for our consumers.”

Meanwhile, former Obama administration officials expressed outrage.

“President Trump’s executive order to roll back vital climate and clean air protections this afternoon is the most brazen and transparent assault on the health of Americans in my lifetime,” said Heather Zichal, former deputy assistant to the president for energy and climate change.

Lisa P. Jackson, who headed the EPA during Obama’s first term and is now Apple’s vice president of environment, policy and social initiatives, said in a statement that “limiting climate protections threatens the certainty businesses need to continue to innovate.”

And several governors said that they would press ahead with their own plans to cut carbon emissions.

Gov. Jay Inslee (D-Wash.) noted in an interview that he had spent part of Tuesday in Snohomish County, heralding the “biggest battery in the world to integrate solar and wind into the grid,” whose development was underwritten in part by state taxpayers.

And California Gov. Jerry Brown (D) said in an interview that he, like Inslee, was prepared to take the new administration to court over its regulatory rewrite. “Gutting the Clean Power Plan is a colossal mistake and defies science itself,” he said. “Erasing climate change may take place in Donald Trump’s mind, but nowhere else.”

Outside the EPA on Tuesday afternoon, protesters shouted and waved signs, biding their time for a larger protest later in the day outside the White House. Inside, some employees watched the president’s remarks on YouTube, while others went for a walk. In the Map Room, Trump sat at a small table and scribbled his signature on the order.

“Come on, fellas. Basically, you know what this is?” Trump said to the coal miners gathered around him. “You know what it says, right? You’re going back to work.”