The agency's director recently traveled to North Korea to pave the way for direct talks between the North Korean leader and President Trump. It "went very smoothly," Trump said.
The Fox News host had earlier been identified as a client of the president's personal attorney, Michael Cohen, whose offices and hotel room were raided by federal prosecutors this month.
President Trump begins two days of meetings with Japanese Prime Minister Shinzo Abe on Tuesday. North Korea's nuclear threat and trade are expected to dominate the discussions.
Inspectors general throughout Washington, D.C., are involved in oversight of everything from the Environmental Protection Agency administrator's travel to ongoing FBI investigations.
The latest action in Syria — which comes shortly after the president said he wanted to withdraw U.S. troops from the country — illustrates the competing impulses that drive his foreign policy.
The executive order, issued late Thursday, comes after months of criticism of the U.S. Postal Service for what the president claims is a money-losing deal to deliver packages for Amazon.