The White House is struggling to prevent a crippling exodus of foreign policy staffers eager to leave before the arrival of the Trump administration, according to current and former officials.

The top level officials in the National Security Council (NSC) are political appointees who have to submit resignations and leave in a normal transition. The rest of the 400 NSC staff are career civil servants on secondment from other departments. An unusual number of these more junior officials are now looking to depart.

Many are concerned by a proliferation of reports about the incoming national security adviser, Michael Flynn. On Wednesday the Washington Post reported that Flynn had improperly shared classified information with foreign military officers. On the same day, CNN reported that the former DIA chief had this week deleted a tweet he had sent out a few days before the election that linked to a fake news story suggesting Hillary Clinton took part in crimes against children.

“Career people are looking get out and go back to their agencies and pressure is being put on them to get them to stay. There is concern there will be a half-empty NSC by the time the new administration arrives, which no one wants,” said one official.

More: White House faces exodus of foreign policy experts ahead of Trump’s arrival