 In 1856, shortly after finishing the St. Mary's River project, Corning was elected as a Democrat to the 35th, 37th and 38th United States Congresses, serving from March 4, 1857, to March 3, 1859, and from March 4, 1861, to October 5, 1863, when he resigned.He was a delegate to the 1860 Democratic National Convention.In 1861, before taking office in Congress, he was a delegate to the Peace Congress in Washington, D.C., but once the Civil War began he took his seat in Congress and, at least initially, supported the Abraham Lincoln Administration.