"The election before us will be the Austerlitz of American politics"

This quote by Roscoe Conkling is referring to the upcoming election as a crucial battle. The Battle of Austerlitz was a significant fight in the Napoleonic Wars, as well as is commonly referred to as the "Battle of the Three Emperors" due to the visibility of Napoleon, Tsar Alexander I, as well as Holy Roman Emperor Francis II. The fight was a decisive victory for Napoleon, as well as Conkling is suggesting that the upcoming election will certainly be a likewise definitive triumph for one side. He is most likely referring to the Republican Party, which he belonged to, and also recommending that the election will certainly be a significant juncture in American national politics. Conkling is recommending that the election will be a major victory for the Republican Party, and will have a long-term effect on the political landscape of the United States.