>>1507768 en.wikipedia.org/wiki/Capital_punishment_by_the_United_States_military
Snippet: "The U.S. Armed Forces Court of Appeals ruled in 1983 that the military death penalty was unconstitutional, and after new standards intended to rectify the Armed Forces Court of Appeals' objections, the military death penalty was reinstated by an executive order of President Ronald Reagan the following year."
If Reagan could reinstate the military death penalty via EO, it seems to me that another EO by DJT could reestablish hanging or firing squad as the method of execution. Uncertain though.