1940 United States Senate election in Wisconsin

The 1940 United States Senate election in Wisconsin was held on November 5, 1940.

Incumbent Progressive U.S. Senator Robert La Follette Jr. was elected to a third term in office over Republican Fred H. Clausen and Democrat James E. Finnegan.

Candidates

 * Robert M. La Follette Jr., incumbent Senator since 1925

Candidates

 * Walter B. Chilsen, former State Assemblyman (1919–21) and editor of the Merrill Daily Herald
 * Fred H. Clausen, farming equipment manufacturer
 * Michael G. Eberlein
 * Glenn Frank, former President of the University of Wisconsin-Madison
 * John P. Koehler, Health Commissioner of Milwaukee
 * William C. Maas
 * Reuben W. Peterson, former State Assemblyman (1937–39)

Campaign
Frank died two days before the primary, on September 15, but remained on the ballot.

Candidates

 * William D. Carroll, former State Senator (1933–37)
 * John Cudahy, former U.S. Ambassador to Poland, Luxembourg, Belgium, and the Irish Free State (write-in)
 * James E. Finnegan, former Wisconsin Attorney General (1933–37)
 * James J. Kerwin

Candidates

 * Fred H. Clausen, farming equipment manufacturer (Republican)
 * James E. Finnegan, former Wisconsin Attorney General (Democratic)
 * Ted Furman (Communist)
 * Robert M. La Follette Jr., incumbent Senator since 1925 (Progressive)
 * Adolf Wiggert (Socialist Labor)