When the Environmental Protection Agency proposed rules regulating carbon dioxide emissions from coal-fired power plants, Scott Pruitt sued. When the Justice Department offered legal status to young undocumented immigrants, Scott Pruitt sued. And when the Obama administration sought to give tax credits to states that hadn’t set up their own health insurance exchanges, Scott Pruitt sued.

Since becoming Oklahoma attorney general in 2010, Pruitt has filed or joined lawsuits against federal agencies at least a dozen times. Even when Oklahoma isn’t an actual party in litigation, the state often submits a legal brief against the federal government. Besides air pollution, immigration and health care, Pruitt has fought federal laws and regulations on banking, contraception and endangered species. These days, whenever states go to court against the Obama administration, the chances are that Pruitt is somehow involved.

Not that Pruitt is alone. During Obama’s presidency, the entire cadre of Republican attorneys general (27 at present) has coordinated cases against federal agencies at an unprecedented pace. But Pruitt is at the center of the action. He has set up a first-in-the-nation “federalism unit,” which seeks to combat instances of federal overreach by every possible means: letters, comments during the rulemaking process, congressional testimony, legal briefs and, most conspicuously, lawsuits. When Pruitt became chairman of the Republican Attorneys General Association (RAGA) in 2012, he took the strategy national by launching the group’s “Rule of Law” campaign to help RAGA members research cases related to state autonomy, the Constitution and federalism. “He’s completed the shift for attorneys general nationally who realize now how important it is for states to push back against the federal government,” says former Nebraska Attorney General Jon Bruning, a Republican ally of Pruitt who left office in January.

The legal justification for Pruitt’s court challenges is almost always related to states’ rights. It’s easy, though, for his critics to presume an alternative explanation. He is, after all, a conservative politician filing lawsuits to undermine the liberal policies of a Democrat in the White House. But Pruitt insists that today’s hyperpartisan world misinterprets him. He claims he is merely trying to reassert limits over executive power and would do the same regardless of the president’s political affiliation. In Pruitt’s view, Congress should make laws and the executive branch should administer them. Everything else should be left to the states. Instead, Pruitt says, “you see federal agencies taking license. That’s simply not how our checks and balances work.”

This isn’t just some academic point for Pruitt. He believes the American system of government is under attack by a president unwilling to respect the constitutional limits of his office. Amid partisan gridlock in Washington, Obama has promised to use “a pen and a phone” to accomplish as much as he can through administrative action. That has won praise from liberals, but it has horrified Pruitt, who sees attorneys general as a critical firewall against federal officials infringing on state sovereignty and making national policy without Congress.

While Pruitt admits that he disagrees with Obama’s positions on immigration, health care and the environment, he insists that those concerns are secondary to a more “transcendental” issue: maintaining the system of government as the framers intended it, with no single branch wielding unilateral control. That mission should matter to Democrats, he argues, because they may one day face a Republican president intent on bypassing a Democratic majority in Congress in the same way. In Pruitt’s view, today’s court battles will affect American governance long after Obama leaves office. “We live in a consequential time,” he says. “Precedent is being set.”

Pruitt and Oklahoma Gov. Mary Fallin (AP)

Pruitt, who is 47 years old, projects a political identity that took root more than a decade ago, when he was a state senator from Broken Arrow, a suburb of Tulsa. He framed his early campaigns around shrinking the size of government. He supported a cut to the state income tax and wanted to adopt a formula that would limit future spending growth. At the time, Oklahoma was one of the few states to offer in-state tuition to undocumented immigrants, and Pruitt was among the chorus of Republicans who wanted to restrict that benefit to citizens. (The state reversed its policy after he left the legislature.)

After three years in the state Senate, Pruitt mounted an unsuccessful campaign for Congress. In 2006, rather than seek re-election, he ran for lieutenant governor and nearly upset the Republican House speaker, losing in the primary by less than 1 percent of the vote.

In his second attempt at statewide office, in 2010, timing helped. Obama wasn’t on the ballot that year, but he might as well have been. Pruitt continually portrayed the president as a big-government Democrat working to increase regulations on health insurance and fossil fuel production. To some degree, Pruitt was tapping into populism that’s always been a part of his state’s politics, says Keith Gaddie, a political scientist at the University of Oklahoma. “Standing up to those fancy Eastern Yankees is very much a tradition in Oklahoma.” Pruitt’s résumé turned out to be an ideal one in a state where voters in both parties largely shared his fears about federal encroachment.

The Republican primary for attorney general focused on the legal challenges to the Affordable Care Act. The outgoing Democratic governor and attorney general both refused to join a multistate lawsuit against the health-care law, with then-Gov. Brad Henry calling it “an exercise in legal futility.” By contrast, both Pruitt and his opponent in the primary promised to join the lawsuit. But Pruitt went further. He pledged to establish the nation’s first federalism unit focused entirely on fighting attempts to expand the federal footprint.

Pruitt’s disclaimers aside, it’s impossible not to interpret the federal-state court battles of recent years as contests of both party and ideology. Empirical research supports that view. Paul Nolette, a political scientist at Marquette University, analyzed 20 years of U.S. Supreme Court cases and found that blocs of state attorneys general were challenging the federal government on a partisan basis much more often than they had in the past.

When attorneys general sued the Clinton administration in the 1990s, the coalitions they created tended to be bipartisan. In instances where most of the challengers came from a single party, they were usually Democrats suing a Democratic president. By comparison, the major lawsuits of today feature a homogeneous slate of Republican attorneys general litigating against the Obama administration, with a similarly homogeneous slate of Democrats filing friendly legal briefs in support of Obama.

Nolette says attorneys general are taking legal positions for political purposes and that both parties are doing it. He gives the example of the two same-sex marriage cases decided by the Supreme Court in 2014. Both parties found legal rationales that fit their political ideologies. A bloc of Democratic attorneys general wanted the court to respect state sovereignty when it meant allowing states to legalize same-sex marriage, but also wanted the court to strike down a California law that banned same-sex marriage. Likewise, Republicans argued for states’ rights to save California’s ban on gay marriage, but invoked federal supremacy to maintain a definition of marriage that excluded gay couples.

Until relatively recently, the office of state attorney general was seen for the most part as free from both ideology and partisanship. But that began to change at the start of the 2000s, when the Republican Party set up a group dedicated to electing conservatives to the post. A few years later, Democrats countered with their own group.

Pruitt continues to reject the insinuation that his work is driven by a partisan agenda. “Opponents want to present it that way,” he says. “It’s not that way at all for me.” Nonetheless, the fact remains that he consistently finds legal justifications for policies popular among conservative Republicans, while challenging policies that his party opposes. From the outside, the lawsuits seem to be less about state sovereignty and more about a broader Republican strategy to upend the president’s domestic policy agenda.

When he isn’t challenging Obama directly, Pruitt frequently can be found weighing in on other disputes that clearly divide liberals from conservatives. Much of the time, these center on religion. As attorney general, Pruitt released an official legal opinion in favor of distributing Bibles in public schools; he defended the installation of a religious monument on state Capitol grounds; and in a legal brief in support of an Oklahoma-based business, Hobby Lobby, he argued that businesses should be able to refuse to cover the cost of employees’ contraception on the basis of religious liberties.

“There are broader trends that have been going on for a few years now where the attorneys general have been far more activist,” Nolette says. “But it still requires some sort of entrepreneur to pick it up and press the extent of the power.” Pruitt has been that kind of entrepreneur.

One example is the King v. Burwell case. The plaintiffs in the case mounted an argument that actually was first embraced by Pruitt. The case hinged on language in the Affordable Care Act that said tax credits were to go to individuals who purchased health insurance through an exchange set up by the state. Yet in practice, the federal government has awarded tax credits through both state-based and federal exchanges. If the tax credits were invalid in states with federal exchanges, the law would unravel. Ultimately lower courts didn’t agree on whether the broader context of the law -- aimed at getting people to sign up for health insurance -- meant that federal agencies could ignore an oversight in the statute. The U.S. Supreme Court decided against Pruitt’s position in late June.

“Dozens of think tanks and attorneys general have been analyzing ways to challenge the law,” says Bruning, the former Nebraska attorney general. “It’s been part of the law for years. Many of us didn’t see it.” While Pruitt himself didn’t come up with the novel argument presented in King v. Burwell, he was the first to use it as the basis of a lawsuit. At the time, the architects of the argument -- Jonathan Adler of Case Western Reserve University Law School and Michael Cannon of the libertarian Cato Institute -- were having trouble getting Republican state officials to mount a challenge based on what seemed like a highly technical reading of the law’s mechanics. Even though other plaintiffs filed lawsuits later on that advanced beyond Pruitt’s case, he was the first attorney general to recognize the potency of Adler and Cannon’s analysis.

So far, Pruitt’s willingness to wade into controversial issues has made him a celebrated figure in conservative circles. In 2014, he ran unopposed for his second term, and he’s on a short list of candidates mentioned prominently for the Oklahoma governorship. But there’s one issue on which he has rankled fellow Republicans. It concerns a lawsuit filed last year by Pruitt and Bruning against Colorado’s legalization and regulation of marijuana. In most of Pruitt’s other high-profile disputes, he has argued against federal intrusion, but in this case, he and Bruning say federal law banning the use of marijuana should preempt state law in Colorado and other jurisdictions that have legalized it. That position strikes many as inconsistent with Pruitt’s efforts to defend state prerogatives. “I think that’s misplaced,” replies Pruitt, who alleges that Colorado’s law has increased illegal drug trafficking in nearby states, including his own. “What about the states’ rights of Oklahoma?”

While both Oklahoma and Nebraska have argued for federal supremacy in the marijuana case, it’s also clear that Pruitt and Bruning disagree with legalization on policy grounds. “It’s about what’s good for our country in the long term,” Bruning says. “I see a slacker culture that makes me think of the fall of Rome. I don’t want to hire employees who smoke marijuana on their lunch break.”

Adler, the law professor who was Pruitt’s ally in the challenge to the Affordable Care Act, summed up conservative dismay over Pruitt’s challenge to Colorado in an op-ed article earlier this year. “It is as if their arguments about federalism and state autonomy were not arguments of principle,” Adler wrote, “but rather an opportunistic effort to challenge federal policies they don’t like on other grounds. It makes Oklahoma and Nebraska look like fair-weather federalists.”