The announcement Tuesday that President Trump is replacing Secretary of State Rex Tillerson with current CIA Director Mike Pompeo adds two more staff changes to Trump’s already highly unstable Cabinet roster.

In November, I compared turnover in Trump’s 24-position Cabinet to turnover in the same jobs in presidential administrations going back to President Jimmy Carter. I found that Trump was the only president since 1977 to replace anyone in those positions in his first year. With Tillerson out and Pompeo moving to a new position in Trump’s second year, the president’s Cabinet now has experienced five changes (three replacements and two new departures).

The departure of a secretary of state is also notable; no one has left that position during a first presidential term since Ronald Reagan was office. Reagan removed Alexander Haig in 1982, replacing him with George Shultz.

The changes in the Trump Cabinet come amid turnover in other high-level staff positions — for example, the recent departure of communications director Hope Hicks. I measured the changes in Trump’s most senior advisers in August and found a lot of turnover there, too.

There have also been several lower-level staffing alterations, including the departure this week of Trump personal assistant John McEntee, reportedly because of security concerns.