Often used other than as an idiom: to assume a given position.
1842, Daniel Davis et al., Davis's Manual of Magnetism:
Now in this case, if the suspended bar were acted upon solely by the north pole of the magnet, it would assume the position AB
1998, Nomination of Kevin Gover: Hearing Before the Committee on Indian Affairs, United States Senate:
President Clinton's nominee to assume the position of Assistant Secretary for Indian Affairs at the Department of the Interior […]
(idiomatic,US,law enforcement) To turn away, with your hands in a visible and unmovable position so that you can be searched
2002, James Harper Walker, Inside Your Local Police:
A day or two later we took down another seller and this time the rookie performs the search. Assume the position! he tells the guy. So the guy leans against the side of the car.