President Trump insists his isn't a White House in chaos, but it's hard to deny the near constant churn of key aides, including Tuesday's announced departure of economic adviser Gary Cohn. A full 43 percent of top-level positions in the Trump White House have seen turnover. That is not normal.

In fact, the Trump White House has had more turnover among senior aides in the first 13 1/2 months of Trump's term than his four most recent predecessors had after two years.

"After two full years, President Obama was at 24 percent and President Bush was at 33 percent," said Kathryn Dunn Tenpas of the Brookings Institution and the White House Transition Project, whose research specialty includes staff turnover. "So, [Trump] already passed them with his first-year turnover. It continues to surge."

In the hours before Cohn's resignation was announced, Trump foreshadowed a shake-up.

"Yeah, there'll be people — I'm not going to be specific — but there'll be people that change," Trump said at a Tuesday afternoon press conference. "They always change. Sometimes they want to go out and do something else."

One would note he was speaking of "people," plural, as in multiple expected departures. Trump tweeted much the same Tuesday morning.

In addition to Cohn's departure, several other staffers have recently left or announced their imminent resignations. Communications director Hope Hicks and Jared Kushner advisers Josh Raffel and Reed Cordish have all announced their departures while staff secretary Rob Porter was ousted after allegations of spousal abuse came to light.

A big question now is: Who will be next? Cohn had assembled a team of policy aides who helped craft the White House infrastructure plan and tax framework. With Cohn leaving, will they stay? History would indicate that when someone at Cohn's level leaves, others follow.

"It's a domino effect. When a senior person leaves, there are other people that leave as well," Tenpas said. "Kind of by necessity because the new person isn't necessarily going to want to work with them."

And if the swirl of Washington chatter is accurate, Cohn isn't the only big-name White House official on the knife's edge. Chief of staff John Kelly, national security adviser H.R. McMaster and adviser/son-in-law Kushner are all reportedly earning the ire of the president.

As of Jan. 20, the one-year anniversary of Trump's inauguration, turnover in top-level White House positions was off the charts, double that of President Ronald Reagan's first year and more than triple the rate of President Barack Obama's first year. Since then, there has been turnover in another six senior-level positions that Tenpas tracks.

"This is an environment that is not suitable for governing. You need people with institutional knowledge, you need expertise," said Tenpas. "There's vacancies on top of vacancies."

Typically, there is much more staff turnover in a president's second year in office than in the first. There was some question of whether in the case of Trump, there had been so many departures in the first year that the pattern would be different and the exit door would swing more slowly in his second year. It is now clear that isn't the case.

"It looks as though turnover continues," Tenpas said. "People are moving to new positions. A lot of people are resigning or leaving. It's unclear when this will cease or whether it's just a continuous process with President Trump."

Why so much turnover? Trump admitted his White House isn't an easy place to work because he fosters an environment of conflict.

"It's tough," Trump said. "I like conflict. I like having two people with different points of view. And I certainly have that. And then I make a decision. But I like watching it. I like seeing it."

In Cohn's case, he was often on the losing end of those policy debates. Trump insisted in a tweet that he will be easy to replace. "Many people wanting the job — will choose wisely!" Trump wrote.

Tenpas has data going back to Reagan's presidency and, in an effort to make apples to apples comparisons, only tracks certain senior positions that have equivalents across administrations. In the Trump administration, she is tracking 65 positions. But turnover in each position only counts once, and if someone changes jobs or gets a promotion, they are not counted twice.

Copyright 2018 NPR. To see more, visit http://www.npr.org/.