A senior State Department official is abruptly leaving his role in the Biden administration. And on his way out, he has sent a scathing internal memo criticizing the president’s use of a Trump-era policy to expel migrants from the southern border.

In a detailed legal memo dated October 2 and obtained by POLITICO, Harold Koh, a senior adviser and the sole political appointee on the State Department’s legal team, called the use of the public health authority known as Title 42 “illegal,” “inhumane” and “not worthy of this Administration that I so strongly support.”

“I believe this Administration’s current implementation of the Title 42 authority continues to violate our legal obligation not to expel or return (“refouler”) individuals who fear persecution, death, or torture, especially migrants fleeing from Haiti,” the memo reads. He added that “lawful, more humane alternatives plainly exist.”