Top officials at the Department of Homeland Security are wondering who will be next to depart the agency after a series of surprise terminations in recent days — and no way of knowing if President Trump is through with the chopping block.

Three senior officials at the 16-year-old agency, including the secretary of the department, have been stripped of their offices. That leaves the country’s border and immigration agencies without directors as the highest number of migrants in more than a decade continues to arrive at the U.S.-Mexico border.