Office of Personnel Management Director Jeff Pon resigned on Friday, according to a White House official who declined to describe his reasoning.

The White House announced Friday afternoon that Margaret Weichert has been appointed as the acting OPM director. The official was unsure if the president intends to nominate a permanent director, but a White House statement noted that Weichert was confirmed by the Senate to her current post as deputy OPM director for budget.

Pon is the latest in a long line of senior Trump administration or White House officials to be fired or resign. President Donald Trump’s senior-level turnover rate is the highest in the modern era, according to several experts who track executive branch staffing.

The White House announced the OPM change during Sen. Susan Collins’ much-anticipated floor speech announcing she would vote in favor of Supreme Court nominee Brett Kavanaugh.