In 1867, the General Assembly of Maryland nominated Swann to succeed John A. J. Creswell to the United States Senate. But, Radical Republicans had gained control of the Congress in 1867, and refused to allow Swann admission to the Senate because he had switched parties. The Democrats in Maryland began to fear that, if Swann left, the Maryland lieutenant governor, a Radical Republican, might place Maryland under a military, Reconstruction government and temporarily disfranchise whites who had served in the Confederacy. Also, they did not want to lose reforms made by Swann with other voting rights. Rather than fight the Radicals in Congress to gain a seat, Swann was convinced by Democrats to remain as governor and turn down the Senate seat.