From The "Biographical Directory of the United States Congress, 1774-2005"
"Leonidas Carstarphen Dyer a Representative from Missouri; born near Warrenton, Warren County, Mo., June 11, 1871; attended the common schools, Central Wesleyan College, Warrenton, Mo., and Washington University, St. Louis, Mo.; studied law; was admitted to the bar in 1893 and commenced practice in St. Louis, Mo.; served in the Spanish-American War; was a member of the staff of Governor Hadley of Missouri, with the rank of colonel; commander in chief of the Spanish War Veterans in 1915 and 1916; elected as a Republican to the Sixty-second Congress (March 4, 1911-March 3, 1913); presented credentials as a Member-elect to the Sixty-third Congress and served from March 4, 1913, to June 19, 1914, when he was succeeded by Michael J. Gill, who contested his election; elected to the Sixty-fourth and to the eight succeeding Congresses (March 4, 1915-March 3, 1933); unsuccessful candidate for reelection in 1932 to the Seventy-third Congress and for election in 1934 to the Seventy-fourth Congress and in 1936 to the Seventy-fifth Congress; resumed the practice of law; died in St. Louis, Mo., December 15, 1957; interment in Oak Grove Cemetery."
I found it curious that he is not listed in the MO Online Database"Soldiers' Records: War of 1812 - World War I" http://www.sos.mo.gov/archives/soldiers/http://www.sos.mo.gov/archives/soldiers/ But it looks like he was enlisted while living in Washington D.C. Has a Pension Card Filed March 9th 1899 in DC has service as C?DC Inf. (? can't mak out) It could be Col DC Infantry. application number 1221,065