What did the strong support of the republican party in the election of 1856 prove? a) the anti-slavery movement in the united states was on the decline. b) the anti-slavery movement in the united states was growing. c) slavery was no longer an important issue to the citizens of the united states. d) the building of a railroad was the most important issue facing the united states. what did the strong support of the republican party in the election of 1856 prove?