At least six White House National Security Council officials have been fired or reassigned, according to several people familiar with the matter, in what appears to be the first significant purge of Donald Trump’s second presidency.

The shakeup at the NSC, which advises the president on the most important security challenges facing the country, comes at a volatile geopolitical moment, one day after the Trump administration slapped major tarrifs on almost every country in the world and as the administration struggles to negotiate an end to the war in Ukraine.

It was not clear exactly why the officials were let go. But three of the sources said several were told there were issues with their background vetting.

One of the sources said there were also concerns about leaks to the media, while two other sources suggested the ouster was aimed broadly at officials who held views that were seen as too interventionist for the liking of Trump’s allies.

On Wednesday, Trump met right-wing conspiracy theorist Laura Loomer, who privately called on the president to fire some NSC staffers. The New York Times was the first to report their meeting, while Axios first reported on the NSC purge on Thursday.