President Trump has appointed Jay Clayton, who served as the top Wall Street enforcer during Mr. Trump’s first term, to be the interim U.S. attorney for the Southern District of New York, the president said in a social media post on Wednesday.

The action came after Senator Chuck Schumer, the New York Democrat and minority leader, said he would block Mr. Trump’s nomination of Mr. Clayton, 58, for the U.S. attorney post, using a prerogative given to home-state senators. Mr. Schumer made his move after weeks in which some liberal Democrats had made scathing attacks on him for doing too little to resist Mr. Trump.

Mr. Trump said in his Truth Social post that he would continue to pursue Mr. Clayton’s Senate confirmation. Mr. Clayton, a lawyer at the firm Sullivan & Cromwell who has never been a prosecutor, served as chairman of the Securities and Exchange Commission from 2017 to 2020.

“During my first term, Jay served with great distinction as the chair of the Securities and Exchange Commission, and earned the respect of everyone,” Mr. Trump said in the post.

The Southern District, which is based in Manhattan, has long been considered one of the most prestigious federal prosecutor’s offices in the country. It is known for handling high-profile cases involving public corruption, national security, international terrorism, fraud on Wall Street and other white-collar crime and sex trafficking.

The district, which includes Manhattan, the Bronx and several upstate counties, has long been referred to jokingly as the Sovereign District, a nod to its prized past independence. Its alumni have included former U.S. attorneys general, F.B.I. directors and countless judges.