Scott Pruitt, former head of the Environmental Protection Agency during a portion of the Trump administration, has filed to run for Senate in Oklahoma.

Pruitt filed paperwork as a Republican this week to run for the U.S. Senate seat being vacated by Sen. Jim Inhofe.

In this May 16, 2018 file photo, then-Environmental Protection Agency Administrator Scott Pruitt appears before a Senate Appropriations subcommittee on the Interior, Environment, and Related Agencies on budget on Capitol Hill in Washington. 

In this May 16, 2018 file photo, then-Environmental Protection Agency Administrator Scott Pruitt appears before a Senate Appropriations subcommittee on the Interior, Environment, and Related Agencies on budget on Capitol Hill in Washington.  (AP Photo/Andrew Harnik, File)

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Pruitt resigned from Trump’s EPA in July 2018 amid a string of controversies that included alleged ethics violations and controversial spending on travel and ties to lobbyists.

Pruitt told The Associated Press on Friday, that he "led with conviction in Washington, D.C." and chalked up the criticism against him as resulting from leading an agency that was the "Holy Grail of the American left."

Sen. Jim Inhofe

Sen. Jim Inhofe, R-Okla., arrives for the Senate Armed Services Committee hearing on the conclusion of military operations in Afghanistan and plans for future counterterrorism operations (Photo By Tom Williams/CQ-Roll Call, Inc via Getty Images) (Tom Williams/CQ-Roll Call, Inc via Getty Images)

"And I made a difference in the face of that," Pruitt, who prioritized the dismantling of several Obama-era regulations during his time at the EPA, said. "I think Oklahomans know when the New York Times and CNN and MSNBC and those places are against you, Oklahomans are for you."

At the time Pruitt stepped down from his position at the EPA, then President Trump praised the "outstanding job" Pruitt had done.

"I will always be thankful to him for this," Trump said.

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Democrats praised the news of Pruitt’s resignation with Vermont Sen. Bernie Sanders calling him the "the worst EPA administrator in the history of the agency" and Delaware Sen. Tom Carper claiming that "history will not look kindly on this era."

Pruitt will face a crowded GOP primary field seeking to replace Inhofe, 87, who shook up Oklahoma politics with his announcement that he would step down in January, just two years into his six-year term. Ten Republican hopefuls have filed to run for the seat, including U.S. Rep. Markwayne Mullin, former Speaker of the Oklahoma House T.W. Shannon, Inhofe’s longtime Chief of Staff Luke Holland, state Sen. Nathan Dahm and Alex Gray, former chief of staff of the National Security Council under Trump.

"As I look at the race, all good folks," Pruitt told reporters at the Oklahoma state capitol after filing paperwork on Friday, according to the Oklahoman. "And I will tell you, from my perspective, I offer the experiences I've had serving in (former President Donald Trump's) cabinet, serving as attorney general, making a difference in behalf of these issues that matter to Oklahomans today and I think matter to this country. And other candidates have their experiences, and they're going to offer their experiences."

Pruitt served as Oklahoma's attorney general from 2011 to 2017 and sued the Environmental Protection agency on multiple occasions during his tenure.

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FILE - In this June 2, 2017, file photo, EPA Administrator Scott Pruitt speaks to the media during the daily briefing in the Brady Press Briefing Room of the White House in Washington. A federal appeals court in Washington says Pruitt overstepped his authority in trying to delay implementation of a 2016 rule requiring oil and gas companies to monitor and reduce methane leaks. In a split decision, the three-judge panel from the U.S. Court of Appeals for the District of Columbia Circuit ruled Monday, July 3, that EPA must move forward with the Obama-era requirement that aims to reduce the planet-warming emissions from oil and gas operations. Pruitt announced in April that he would delay by 90 days the deadline for oil and gas companies to follow the new rule, which they were required to comply with starting last month. (AP Photo/Pablo Martinez Monsivais, File)

EPA Administrator Scott Pruitt speaks to the media during the daily briefing in the Brady Press Briefing Room of the White House in Washington on June 2, 2017. (AP Photo/Pablo Martinez Monsivais, File)

Former Democratic U.S. Rep. Kendra Horn was the only Democrat to file for the seat by early afternoon on Friday, the final day of the three-day candidate filing period.

Because of Inhofe’s announcement, both of Oklahoma’s U.S. Senate seats are up for grabs this cycle. Current U.S. Sen. James Lankford is seeking another six-year term. Lankford will face Tulsa pastor Jackson Lahmeyer in the GOP primary. Four Democrats, a Libertarian and an independent also filed this week to seek the post.

Pruitt did not immediately respond to a request for comment from Fox News. 

Associated Press contributed to this report