"Has this ever happened before?
Yes and no.
We could not find another instance where a president had singled out particular members of Congress and denied their CODEL request. It's also unprecedented that a president would alert the public to CODEL travel plans to a war zone, which according to Pelosi spokesman Drew Hammill, raised the State Department's threat level in the trip's security assessment.
There is precedent for speakers preventing particular members of Congress from traveling overseas. In 2015, Speaker John Boehner, an Ohio Republican,
disapproved Texas GOP Rep. Louie Gohmert's planned trip to Egypt and Africa. (Boehner did the same to Republican Rep. Steve King of Iowa earlier that year.)
In the past, members of Congress have been limited in their ability to travel to certain countries due to military operations in the area and resource concerns.
According to retired Rear Admiral and CNN analyst John Kirby, lawmakers were temporarily denied CODEL requests to war zones during President Barack Obama's tenure due to sequestration and security concerns from military officials. Though, Kirby noted, the ban applied to both Republicans and Democrats and did not single out a particular member of Congress, as Trump did before his administration issued a blanket ban."