President Donald Trump’s first national security adviser, Michael Flynn, was fired after 25 days on the job. Two high-profile campaign aides who followed him into the White House, Reince Priebus and Steve Bannon, were gone before summer’s end. And his third communications director’s tenure is still remembered around the West Wing as “Scaramucci Week.”

Those are just a few of the first-year departures from high level positions in the Trump administration, which has been marked by a level of staff turnover unprecedented in the modern era.

According to Kathryn Dunn-Tenpas, a senior fellow at the Brookings Institution who has tracked White House turnover rates over three decades, the Trump administration’s 34% turnover rate—21 of the 61 senior officials she has tracked have resigned, been fired or reassigned—is much higher than that of any other administration in the last 40 years, which is as far back as Ms. Dunn-Tenpas’s analysis goes. The presidency with the next-highest first-year turnover rate was Ronald Reagan’s , with 17% of senior aides leaving the administration in 1981.