Insurrection Act, 1807

[I]n all cases of insurrection, or obstruction to the laws, either of the
United States, or of any individual state or territory, where it is
lawful for the President of the United States to call forth the militia
for the purpose of suppressing such insurrection, or of causing the
laws to be duly executed, it shall be lawful for him to employ, for
the same purposes, such part of the land or naval force of the
United States, as shall be judged necessary, having first observed
all the pre-requisites of the law in that respect.
Insurrection Act of 1807, ch. 39, 2 Stat. 443, 443