Mitigate is sometimes used as an intransitive (followed by against) where militate might be expected. Even though Faulkner used it <some intangible and invisible social force that mitigates against him — William Faulkner> and one critic thinks it should be called an American idiom, it is usually considered a mistake.
Examples of MITIGATE
Emergency funds are being provided to help mitigate the effects of the disaster.
medicines used to mitigate a patient's suffering
At the far end of the room is a sliding glass door, taped with an X to mitigate shattering. The framing is flimsy, and rattles from mortar rounds even a half mile away. —William Langewiesche, Atlantic, May 2005
… a genre novel whose inevitable cinematic ending doesn't mitigate the visceral and emotional power of what has come before. It lingers in the memory like a very bad dream. —Joyce Carol Oates, New York Review of Books, 14 Aug. 2003
For 65 holes Norman dominated the classic rolling fairways and small, subtle greens of Olympic … with driving and iron play so solid that it mitigated mediocre putting. —Jaime Diaz, Sports Illustrated, 8 Nov. 1993