United States Senate election in Wisconsin 1988 Tags: Election.The 1988 United States Senate election in Wisconsin took place on November 8 1988. Incumbent Democrat U.S. Senator William Proxmire decided to retire instead of running for re-election to a sixth full term. Democrat Herb Kohl won the open seat. thumbnail start date 1988-11-08 title United States Senate election in Wisconsin 1988 Learn more... Loading...