I can not think of any situation in which the provost marshal would be able to arrest the President.

The Provost Marshal is the officer in the armed forces who is in charge of the Military Police.

criminal investigation division, part of the Provost marshal element (military police)

Chris Provost is 6' 1 1/2".

From the Online Etymology Dictionary:

; provost : O.E. profost, from M.L. propositus (reinforced by O.Fr. cognate provost), from L. propositus, præpositus "a chief, prefect" (cf. O.Prov. probost, O.H.G. probost, Ger. Propst), lit. "placed before, in charge of," from pp. of præponere "put before" (see preposition). Provost marshal first recorded 1513.