Poultry giants Tyson Foods Inc. and Cargill Corp. got what they hoped for when Scott Pruitt was elected Oklahoma's attorney general in 2010.

Under his predecessor, Oklahoma had accused 14 poultry companies of allowing nutrient runoff to pollute the Illinois River Basin. Five years in the making, the federal case was a critical chapter in the nearly 20-year battle to enforce water quality standards in northeastern Oklahoma.

Pruitt (R), whom President-elect Donald Trump nominated yesterday to lead U.S. EPA, scrupulously slow-walked the litigation when he became Oklahoma's top lawyer. And in 2013, Pruitt announced that his state and Arkansas would conduct a three-year study before taking any further action on the pollution problem.

Pruitt has been a strong proponent of deregulation for most of his elected career. As leader of coordinated efforts by Republican officeholders to sue the EPA, he has advocated the dismantling of rules requiring cuts to carbon emissions from the electric power and gas sectors and curtailing U.S. enforcement powers.

"I've fought for 6 years against the ACA, WOTUS, Immigration & the Clean Power Plan. Which should #Trump tackle first?" Pruitt said on Twitter last month, using acronyms for the Affordable Care Act and EPA's proposal to expand the Clean Water Act's definition of "waters of the United States."

"That's probably going to be a hallmark under the Trump administration," said Brendan Collins, an attorney at Ballard Spahr LLP in Philadelphia who specializes in utility and energy litigation.