Charles Curtis was a Protestant. Further research is needed in order to identify his specific denominational affiliation.
From: Political Graveyard website (http://politicalgraveyard.com/bio/curtis.html#R9M0IU3Z0; viewed 29 November 2005):
Curtis, Charles (1860-1936) - also known as "Square Shooter"; "The Whisperer" - of Topeka, Shawnee County, Kan. Born in a log cabin at Eugene (now part of Topeka), Shawnee County, Kan., January 25, 1860; his mother was one-quarter blood Kansa/Osage Indian. Great-great-great-grandson of "White Hair" Pawhuska (Great Osage chief for whom Pawhuska, Okla. is named); married, November 27, 1884, to Annie E. Baird. Republican. Lawyer; U.S. Representative from Kansas, 1893-1907 (4th District 1893-99, 1st District 1899-1907); resigned 1907; U.S. Senator from Kansas, 1907-13, 1915-29; delegate to Republican National Convention from Kansas, 1908; candidate for Republican nomination for President, 1924; Vice President of the United States, 1929-33; defeated, 1932. English, French, and Kansa/Osage Indian ancestry. Died of a heart attack, in Washington, D.C., February 8, 1936. Interment at Topeka Cemetery, Topeka, Kan.