WASHINGTON—U.S. Securities and Exchange Commission (SEC) Commissioner Elad Roisman will be named the agency’s acting head, after Chairman Jay Clayton officially announced he was stepping down on Dec. 23, according to a tweet by fellow Republican Commissioner Hester Peirce on Dec. 24. “Congratulations, Chairman Roisman! I look forward to your leadership of the SEC,” Pierce wrote. Roisman, the SEC and the White House didn’t immediately respond to requests for comment. The move by Clayton was widely expected as he had previously indicated his desire to leave the agency by the end of the year. Roisman, who has been a commissioner since 2018, would run the agency, which oversees public companies, brokers, Wall Street banks, and investment funds, until a new chair is selected. Clayton, a former Wall Street lawyer, was appointed by President Donald Trump in 2017. His departure leaves the SEC, which is led by political appointees who vote …