As the United States faces possible retaliatory attacks from Iran, a “brain drain” in top Justice Department and FBI national security and counterterrorism units could reduce their ability to prevent potential terror and cyber attacks from Tehran, according to six former senior DOJ and FBI officials.

Staff levels in the DOJ National SecurityDivision’s Law and Policy section have dropped by as much as two-thirds, two former DOJ officials said. Its counterintelligence and export control section — which tracks foreign espionage in the U.S. by Iran and other foreign rival — has lost about a third of its workforce, two former DOJ official said.

A former senior FBI official said he was aware of at least 20 national security personnel who had left the bureau in the last 3 months.