Oklahoma Attorney General Scott Pruitt arrives at Trump Tower in New York in December to meet with the president-elect. (Jabin Botsford/The Washington Post)

In the spring of 2010, Republican Scott Pruitt announced his candidacy for Oklahoma attorney general with a simple promise: He would fight the federal government at every turn.

“The attorney general in the respective states is really the only place that you can respond to the aggressiveness coming out of Washington,” Pruitt, a former state senator and past co-owner of Oklahoma City’s minor league baseball team, said that day. “I intend to use the office for that reason.”

He has, with gusto.

Nowhere has his resistance been more evident than in his attacks on the Environmental Protection Agency — which President-elect Donald Trump has nominated him to run. Pruitt has sued the EPA repeatedly during the Obama administration, challenging the agency’s legal authority to regulate toxic mercury pollution, smog, carbon emissions from power plants, and the quality of wetlands and other waters.

That combative approach has won him praise from some fellow Republicans and the oil and gas firms that have helped fund his efforts, as well as from Trump, who has criticized the EPA for what he calls burdensome and unnecessary regulations. But it has horrified environmental advocates, who accuse Pruitt of being a climate-change denier and little more than an arm of the fossil fuel industry.

“We see him time and again appearing to side with industry and large corporations rather than fulfilling his duty to protect the general public,” said Johnson Bridgwater, director of the Oklahoma chapter of the Sierra Club. “It’s like putting an atheist in the role of the pope.”

[Trump’s nominee to head EPA has opposed the Chesapeake Bay cleanup]

Upon taking office in 2011, Pruitt dismantled a specialized environmental protection unit that had existed under his Democratic predecessor and established a first-of-its-kind “federalism unit” to push back on “unwarranted regulation and systematic overreach” by Washington. Environmental cases­ have since been handled by the state’s solicitor general, which, according to a Pruitt spokesman, “has a distinguished track record of successful settlements.”

Pruitt, whose confirmation hearing is set for Wednesday before the Senate Committee on Environment and Public Works, declined an interview request for this article.

That work battling the federal government quickly became a strategy Pruitt took national. He helped to lead the Rule of Law Defense Fund, a privately funded group of attorneys general that fought the Obama administration on such issues as the Affordable Care Act, Wall Street reforms, and efforts to extend overtime pay to more workers.

At the same time, Pruitt and his Republican counterparts delved into clashes in individual states: Opposing a Maryland weapons ban. Helping California egg farmers defeat regulations. Arguing against an EPA cleanup plan of the Chesapeake Bay.

“I wouldn’t pick anybody who had actively sued the [EPA] to be its administrator,” said Drew Edmondson, the longtime Oklahoma attorney general whom Pruitt replaced in 2010. Yet he acknowledged that Pruitt had done precisely what he campaigned to do: “That was his philosophy going in. He didn’t make any bones about the fact he was going to pick fights with the federal government.”

Elected in tea party wave

Pruitt, 48, grew up in Lexington, Ky., the oldest of three children. A standout high school baseball player, he was recruited to play Division I baseball at the University of Kentucky but later transferred to Georgetown College, a small Christian school near Lexington.

After law school at the University of Tulsa, he settled in the Sooner State and in 1998 won a seat in the Oklahoma Senate. He ran unsuccessfully for a seat in Congress in a 2001 special election and, after two terms in the legislature, lost a bid to become lieutenant governor.

For the next several years, Pruitt worked as a managing partner of the Triple-A affiliate Oklahoma City ­RedHawks. In 2010, despite little experience as a litigator, he jumped at the chance to run for attorney general.

“It was the tea-party-wave election,” said Keith Gaddie, a University of Oklahoma political science professor. “The money people were lining up with him.”

[Trump victory reverses U.S. energy and environmental priorities]

He rarely sought out local environmental ­cases, choosing instead to contest the EPA’s authority and push for more discretion for states and the energy industry, said Gaddie, who described Pruitt as part of a generation of Republicans who “grew up at the altar of Ronald Reagan. They really took this federalism stuff to heart: Government is not the solution; ‘government is the problem.’ ”

Pruitt’s personal finances­ pale in comparison with those of other Trump Cabinet nominees, who include millionaires and billionaires. In ethics disclosures, he listed an investment portfolio valued between $420,000 and $1 million, with debt between $500,000 and $1 million involving a mortgage on his home.

At First Baptist Church Broken Arrow, where Pruitt and his wife are active members, senior pastor Nick Garland said he doesn’t recognize the man being demonized by environmental groups.

“Scott’s a man with children, he’s got a family. He’s not interested in polluted streams and dirty air and oil flowing in an irresponsible manner,” Garland said. But, he added, “Scott’s a man of law. I think one of the things that has most troubled him in recent years is an overreach in the law” by the federal government.

The pastor expects Pruitt to surprise some critics should he be confirmed to lead the EPA.

“He’s fair, he hears both sides, he’s rational,” Garland said. “He’s seeks conversation with folks on the other side of any issue.”

Competing campaigns

A fierce campaign by environmental groups to block Pruitt’s confirmation has labeled him #PollutingPruitt on social media and faulted him for questioning the need for urgent action on climate change. The groups have pointed to a 2014 New York Times report detailing how a letter he sent to the EPA, accusing it of overestimating air pollution from natural gas drilling, was written by lawyers for Devon Energy.

“That’s actually called representative government in my view of the world,” Pruitt later said of the letter.

Critics also point to what he hasn’t done at home. His predecessor, for instance, sued to prohibit poultry companies in neighboring Arkansas from dumping tons of chicken manure that was polluting waters in northeastern Oklahoma. But instead of pushing a federal judge to rule and potentially award millions of dollars in damages, Pruitt took a different tack once in office: He forged a deal with Arkansas to study the problem further. The legal case remains unresolved.

[Scientists are frantically copying U.S. climate data, fearing it might vanish under Trump]

“Regulation through litigation is wrong in my view,” Pruitt told the Oklahoman newspaper.

Scott Thompson, the current head of the state’s Department of Environmental Quality, praised Pruitt’s “deftness at moving complex environmental issues mired in protracted litigation toward workable solutions.”

But others argue that Pruitt largely overlooked environmental problems in Oklahoma. The Environmental Integrity Project, an advocacy group, recently reviewed more than 700 news releases from Pruitt’s six years as attorney general and found no mention of actions to enforce environmental laws amid the announcements about embezzlers, Medicare cheats and his many EPA lawsuits.

“The fact is, he has not stood up for the people of Oklahoma that have to breathe the air and drink the water,” said Mark Derichsweiler, who retired in 2015 after four decades at the state’s Department of Environmental Quality. “He’s been on the side of the big polluters and the energy conglomerates.”

Pruitt’s office provided a list of about a dozen cases that it said detailed his work protecting state waters and holding polluters accountable, although some cases preceded him. The spokesman noted Pruitt’s representation of the state’s Department of Wildlife Conservation in dealing with fish kills involving pollution, his support of Superfund cleanups and his handling of unspecified “citizen complaints regarding environmental and pollution issues.”

Organizations such as the Sierra Club and the Environmental Defense Fund — which has never before opposed an EPA nominee — have spent large sums on television and online ad campaigns, hoping to pressure senators from both parties to oppose Pruitt.

Those groups and others point to the more than $300,000 Pruitt has received from the oil and gas industry since 2002 as signs that his loyalties lie with corporate interests. They also note the vastly larger amounts that have flowed to the Republican Attorneys General Association, which Pruitt also led, from Koch Industries, ExxonMobil, Murray Energy and other firms.

Yet powerful forces, including the American Petroleum Institute, are pushing his confirmation.

The conservative America Rising Squared, an arm of the Republican super PAC America Rising, recently launched ConfirmPruitt.com, with videos, op-eds, fact sheets and a petition. There also is Protecting America Now, which recently sprang up to support Pruitt. A flier from the group, obtained by Politico, warned that millions of dollars are needed to counter anti-Pruitt efforts from “anti-business, environmental extremists.”

Last week, a coalition of nearly two dozen conservative advocacy groups backed his nomination, writing that he has “demonstrated his commitment to upholding the Constitution and ensuring the EPA works for American families and consumers.”

And on Friday, frustrated by the latest federal regulation of vehicle fuel standards, the National Association of Manufacturers announced a seven-figure, multistate advertising campaign to press for Pruitt’s confirmation.

[Trump transition team for Energy Department seeks names of employees involved in climate meetings]

Pruitt and his supporters have maintained that his fights with the EPA aren’t ideologically driven but reflect a deeply held conviction about the separation of powers: Congress makes laws. The executive branch administers them. And the rest should be left to the states.

“The states are not a vessel to carry out the desires of EPA,” Pruitt said in a speech two years ago. “The states are actually there to make important decisions.”

Given his hostility toward the EPA, it’s no surprise that his selection has caused angst inside the agency’s Pennsylvania Avenue headquarters. William Ruckelshaus, a past EPA administrator under Presidents Richard Nixon and Ronald Reagan, urges Pruitt to move cautiously. Even if he wants to dismantle President Obama’s policies, he would be wise to protect the integrity of EPA scientists and recognize that the agency has an important mission, Ruckelshaus said.

“An effective and strong and highly competent EPA is a benefit to this country,” Ruckelshaus stressed. “And we ought to keep it that way.”

Darryl Fears contributed to this report.