missouri governor claiborne fox jackson had been elected in 1860 on the ticket of the pro-union douglas faction of the democratic party, but privately supported secession. since the constitutional convention had voted against secession, jackson and his fellow secessionists decided to carry it out by seizing st. louis by force and presenting the people of missouri with a "fait accompli". the most significant obstacle was the st. louis arsenal, which was heavily fortified with thick walls.