As the union begins to crumble, Treasury Secretary Dix orders a revenue cutter in New Orleans back North; the captain refuses, and Dix sends this telegram to his agent in the South:

At a time when the outgoing Buchanan administration was doing little to avert the ongoing crisis of Southern secession, Dix’s order electrified both sides of the conflict. (See this NYTimes article for commentary & context.) It also made the previously little-regarded Dix famous, even though the cutter in question eventually did lower its flag & become a Confederate ship!
As late as 1872, during his victorious run for Governor of New York, Dix went by the nickname “Old ‘Shoot Him On The Spot’”!