West Virginia Solicitor General Elbert Lin, who led his state’s litigation fight against the Obama administration’s signature Clean Power Plan and oil and gas methane standards, is leaving his post, according to the state’s attorney general, Patrick Morrisey.

Lin, a Yale Law School graduate and a former clerk to Justice Clarence Thomas, has been rumored to be in line for a federal judgeship either at the district or circuit court level, but Morrisey said he is returning to the private sector. He was also a clerk to a conservative favorite, Judge William Pryor of the U.S. Court of Appeals for the Eleventh Circuit, who is on President Donald Trump’s list of potential U.S. Supreme Court nominees.

“Elbert played a major role in many of the office’s fights against federal overreach, including our historic and unprecedented victory at the U.S. Supreme Court halting the so-called Clean Power Plan,” said Morrisey in a statement, referring to the high court’s stay of the plan pending a decision in the D.C. Circuit.

“We are very sorry to see him go, but after serving as solicitor general for more than four years he has decided to return to the private sector. We appreciate his and his family’s public service.”

Before becoming solicitor general, Lin, the son of immigrants from Taiwan, was a partner in Wiley Rein where he focused on appellate matters and challenged the Federal Communications Commission’s first “net neutrality” decision. He also previously served as a trial attorney in the U.S. Department of Justice. A Wiley Rein spokeswoman said the firm could not comment on whether Lin is returning.

In the spring, Lin reportedly was among a large group interviewed by the White House Counsel’s Office for a vacancy on the D.C. federal district court. There is also a vacancy on the U.S. District Court for the Northern District of West Virginia.