Rep. David Obey’s (D-Wis.) surprise retirement announcement left his seat wide open and brought national party attention to Wisconsin.

The party favorites won their respective nominations Tuesday night.

State Sen. Julie Lassa won the Democratic primary with 84 percent of the vote. Sean Duffy won the GOP nomination with 67 percent of the vote.

Duffy, a former cast member of the MTV's "Real World," has become a favorite of the national GOP, which is spending money on his behalf. House Minority Leader John Boehner (R-Ohio) campaigned for him in late August. 

The Democratic Congressional Campaign Committee made its first independent expenditure ad of the cycle in this race, running an ad against Duffy.