According to reports, Trump himself ordered the move out of frustration over leaks.
Donald Trump's new national security adviser said Thursday that he wants to reduce the White House foreign policy staff by half.
Robert O'Brien said that during the Obama administration the number of staffers swelled to more than 100.
He told employees at a National Security Council town hall late Thursday that he wants to bring the staff level back to where it was when Condoleezza Rice was national security adviser for President George W. Bush.
"That was about 100 staffers to give policy advice to the president and to help implement his decisions," O'Brien said on Fox Business' "Lou Dobbs Tonight."
"And that was with two wars going on" in Iraq and Afghanistan, he said.
"It just ballooned into a massive, you know, bureaucracy ... under the last administration."
The size of the NSC has fluctuated over the years. O'Brien did not it say how he planned to cut the staff. Many staffers are detailed to the NSC from other government agencies so the reductions could be made by not replacing them when their tours are over and they return to other agencies.
According to CNN, the NSC cuts were ordered by Trump, who "was frustrated by damaging leaks of information that he suspected came from agency staffers seconded to the NSC."
"O'Brien himself did not focus on leaks as the reason for the cuts, and said no one was being specifically targeted with these cuts. But one White House official said that leaks are a primary reason driving the change," CNN reported.
As the outlet noted, Trump has condemned "leakers" in the past as "traitors and cowards," promising in May to "find out who they are!"
The decision comes amid a burgeoning scandal over Trump's efforts to pressure Ukraine to investigate his political rival, former Vice President Joe Biden, and Biden's son Hunter.
Trump has claimed his requests were all above board and focused on rooting out corruption in the country.
A whistleblower complaint made public last month claimed White House officials had specifically worked to conceal a conversation between Trump and Ukrainian President Volodymyr Zelensky about an investigation into Biden by hiding it in a highly classified codeword system, accessible to only a handful of people.
Experts have said such a move would have been unusual, though the whistleblower claimed this happened on more than one occasion.
Trump also came under fire for allegedly withholding military aid to Ukraine in exchange for an investigation into Biden. He has emphatically denied this allegation, though a trove of text messages released earlier this month by House committees pursuing an impeachment inquiry into the matter show several diplomats discussing the alleged quid pro quo openly.