Jeffrey Clark Was Considered Unassuming. Then He Plotted With Trump.

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

He is not known for being understated on the topic of himself. Where the typical biography on the Justice Department website runs a few paragraphs, Mr. Clark’s includes the elementary school he attended in Philadelphia, a topic he debated in college and that he worked for his college newspaper, The Harvard Crimson.

After graduating from Harvard in 1989, Mr. Clark earned a master’s degree in urban affairs and public policy from the Biden School of Public Policy at the University of Delaware in 1993 and a law degree from Georgetown University in 1995. He clerked for an appeals court judge, Danny Boggs, who was known for giving prospective clerks quizzes that tested not just 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 stint in the Justice Department’s environmental and natural resources division during the Bush administration, before returning to Kirkland in 2005 as a partner, but not one with an equity stake in the firm, according to a person who worked closely with him at the law firm.He held the title of “non-equity partner,” which meant that he did not share in the firm’s profits or make leadership decisions.

When Mr. Clark returned to the Justice Department as the head of the environmental division in 2018, he flew under the radar. Like other Republican officials, he narrowly interpreted the division’s legal authority and had a typically tense relationship with career lawyers when it came to enforcing anti-pollution laws.

In one instance, Mr. Clark held up Clean Water Act enforcement cases because of a pending matter before the Supreme Court that career lawyers felt did not directly relate to their work, according to a lawyer with knowledge of those cases. The Supreme Court was hearing a matter that involved discharges that flowed through groundwater before reaching waters regulated by the federal government, and the department was working on a case that involved flows over land.

His employees believed that Mr. Clark hoped the court would curtail the law’s reach in a way that would apply to overland spills, too, but by a 6-to-3 ruling, it did not.