Which event in Charles Sumner's life caused him to be attacked in the U.S. Senate in May 1856? A. His efforts to help organize the new Republican Party B. His abolitionist efforts, including standing against the Fugitive Slave Laws and the Kansas-Nebraska Act of 1854 C. His antislavery speech, where he singled out Senator Butler of South Carolina D. His support of President Lincoln’s Emancipation Proclamation