Irving Katz, "Belmont, August," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00092.html.
With unlimited energy and ambition and a willingness to spend money, Belmont set out early on a career in politics. Influenced mainly by his wife's uncle, John Slidell, a powerful Louisiana politician of the antebellum and Civil War periods, Belmont became the New York manager of James Buchanan's unsuccessful campaign for the 1852 Democratic presidential nomination. Franklin Pierce, the eventual nominee, won the presidency and rewarded Belmont, who had contributed generously to Pierce's presidential campaign, by appointing him minister to the Netherlands. During his tenure at The Hague (1853-1857), Belmont negotiated successfully a commercial treaty, designed to open the Dutch East Indies to American trade, and a criminal extradition treaty between the two countries. He also played a behind-the-scenes role in drafting the Ostend Manifesto (Oct. 1854), a diplomatic initiative that he hoped would lead to American acquisition of Cuba. Belmont supported Buchanan's successful bid for the 1856 presidential nomination, but when Buchanan refused Belmont's request to be named minister to Spain, the banker resigned his diplomatic post, returned to New York, and shifted his allegiance to Buchanan's major Democratic antagonist, Illinois senator Stephen A. Douglas.