Robert Emmet Tehan Sr. was born in Milwaukee, Wisconsin on January 7, 1905, the son of James E. and Mary (Ryan) Tehan. He attended Marquette University, receiving his BA in 1927 and a law degree in 1929. Tehan practiced law until his election to the Assembly in 1936 as a Democrat from the Fourth District. He was re-elected in 1938 and 1940, also serving as Democratic floor leader. In 1942, Tehan was elected to the state Senate from the Ninth District; and was re-elected in 1946.
Tehan was very active in the Democratic Party, and during the 1930s, he was considered one of the most prominent Democrats in the state. In 1944, he was elected state chairman, a position of considerable political influence because of the small number of Democrats holding statewide office in Wisconsin. In 1945, and again in 1948, he was elected to the post of national committeeman.
Unlike many of the conservatives active in the Wisconsin Democratic Party, Tehan supported the more liberal policies of the national administration. In the late 1940s, he actively recruited young liberals into the revitalized Democratic Organizing Committee (DOC). In 1948, his well-known feud with Charles P. Green paralleled the liberal-conservative struggle within the state party. Tehan also gained press attention because of his 1946 repudiation and expulsion of from the Democratic Party of Edmund V. Bobrowicz, suspected of Communist affiliations.
In 1948, Tehan's somewhat heavy-handed tactics were instrumental in consolidating support for President Harry S. Truman in Wisconsin at a crucial point in the presidential primaries. In 1949, partially in return for the help received in the 1948 election, Truman appointed Tehan to the United States District Court for the Eastern District of Wisconsin. In 1971, Tehan went into semi-retirement. He died in 1975 at the age of 70.
