Robert Charles Winthrop was an American lawyer, philanthropist, and Whig Party politician who represented Massachusetts in the United States House and Senate from 1840 to 1851. He served as the 18th Speaker of the United States House of Representatives and was a political ally and colleague of Daniel Webster. After a rapid rise in Massachusetts and national politics and one term as speaker, Winthrop succeeded Webster in the Senate. His re-election campaign resulted in a long, sharply contested defeat by Charles Sumner. He ran for Governor of Massachusetts in 1851 but lost due to the state's majority requirement, marking the end of his political career and signaling the decline of the Massachusetts Whig Party.

Charles Sumner was an American lawyer, politician, and statesman who represented Massachusetts in the United States Senate from 1851 until his death in 1874. Before and during the American Civil War, he was a leading American advocate for the abolition of slavery. He chaired the Senate Foreign Relations Committee from 1861 to 1871, until he lost the position following a dispute with President Ulysses S. Grant over the attempted annexation of Santo Domingo. After breaking with Grant, he joined the Liberal Republican Party, spending his final two years in the Senate alienated from his party. Sumner had a controversial and divisive legacy for many years after his death, but in recent decades, his historical reputation has improved in recognition of his early support for racial equality.