Yet in an interview with Fox News on Wednesday, Pruitt denied any knowledge of the raises. He claimed that he had only “found out about the issue yesterday,” and said “[his] staff” was responsible for granting them. Pruitt said upon being briefed, he “corrected the action” and “walked back” the raises.

Carper and Whitehouse wrote to the IG that Pruitt’s Fox interview “raises several troubling questions.”

“If Pruitt’s statements to Fox News were accurate, then one or more EPA officials other than the Administrator appointed and fixed the compensation of these individuals absent direction from or knowledge of the Administrator. This could indicate a serious breakdown of internal controls on the appropriate use of this authority,” they wrote.

“If Pruitt’s statements were false,” the letter continues, “then the SDWA hiring authority may have been intentionally abused under the direction of the Administrator to award large raises to his favored aides.”

The letter comes as Pruitt faces heightened ethical scrutiny over many of his decisions as EPA secretary. Five EPA officials—including Kevin Chmielewski, a political appointee and an early employee of Trump’s presidential campaign—seemed to suffer retaliatory demotions or reassignments after they questioned Pruitt’s handling of taxpayer money or the agency, The New York Times reported Wednesday.

The EPA’s internal ethics watchdog also expanded the scope of a review into Pruitt’s use of a $50-per-night condo on Capitol Hill, which was owned by the wife of a top energy lobbyist. On Tuesday, a lawyer for the agency’s Ethics Office said in a memo that he did not have all the facts about Pruitt’s use of the space when he initially approved the lease last week. In interviews with conservative outlets this week, Pruitt had repeatedly cited the watchdog’s approval of the arrangement.

Yet despite the national attention, Pruitt appears to have held onto the support of his most important ally: President Trump.

“I think Scott has done a fantastic job. I think he’s a fantastic person,” the president told reporters on Air Force One Wednesday afternoon. “You know, I just left coal and energy country. They love Scott Pruitt. They feel very strongly about Scott Pruitt.”

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Elaina Plott is a former staff writer at The Atlantic, where she covered the White House. Connect Twitter