Some of Mr. Clark’s staff said he could be pedantic. As a manager, he made no move to hide when he had little respect for the opinions of his career subordinates.

He’s not known to be an understatement about himself. Where the typical biography on the Justice Department website has a few paragraphs, Mr. Clarks includes the elementary school he attended in Philadelphia, a subject which he debated in college and which he worked for his college newspaper The Harvard Crimson.

After graduating from Harvard in 1989, Mr. Clark earned a Masters in Urban Affairs and Public Policy from the University of Delaware’s Biden School of Public Policy in 1993 and a law degree from Georgetown University in 1995. He worked as a court clerk to Judge Danny Boggs, who was known for giving quizzes to potential employees that tested not only their knowledge of the law but also a range of esoteric trivia.

Mr. Clark then worked for Kirkland & Ellis from 1996 to 2001, followed by a position in the Department of Justice’s Environment and Natural Resources Division during the Bush administration before returning to Kirkland as a partner in 2005, but not as a party. who worked closely with him in the law firm. He held the title of “non-equity partner,” which meant that he did not participate in the firm’s profits or make leadership decisions.

When Mr Clark returned to the Department of Justice as head of the environment in 2018, he was under the radar. Like other Republican officials, he interpreted the department’s legal authority narrowly and maintained a typically strained relationship with professional attorneys when it came to enforcing anti-pollution laws.

In one case, Mr. Clark has held the Clean Water Act enforcement cases on a matter pending in the Supreme Court that a lawyer with knowledge of the cases believed was not directly related to their work. The Supreme Court heard a matter relating to discharges flowing through the groundwater before they reached federal government regulated waters, and the department was working on a case involving currents over land.

His staff believed that Mr. Clark was hoping the court would narrow the scope of the law in a way that would apply to overland pollution. but by a 6-to-3 judgment it didn’t.