Updated at 1:10 p.m. ET
Sen. Herb Kohl of Wisconsin announced his retirement today, making him the sixth senator from the Democratic caucus who won't be seeking re-election next year.
"Even though I continue to love this job, I have decided that the time has come to give someone else the opportunity to serve," Kohl said at his Milwaukee Senate office this morning. "Therefore, I am announcing today that I will not seek another term as your Senator. Rather, I will devote all my energy and time in the next 19 months to continuing to serve the people of our state."
The fourth-term senator's retirement could create a competitive Senate contest in what will already be a challenging year for Democrats. The Democratic party currently holds 53 seats in the Senate and must defend 23 seats in the 2012 election. Republicans, by contrast, must defend only 10 seats.
Brian Walsh, a spokesman for the National Republican Senatorial Committee (NRSC), said in a statement that Kohl's retirement "further dilutes the ability of national Democrats to go on offense, while they fight to maintain their dwindling Senate majority."
"Senator Kohl's retirement, just like his Democrat colleagues who stepped aside before him, immediately presents another key opportunity for Senate Republicans next year," Walsh said.
Wisconsin has, over the past year, proven to be a fiercely competitive political battleground. Republicans made strong gains in the 2010 midterm elections, winning a Senate seat and the governor's office, among other races. But as the Wisconsin GOP attempted to institute its agenda, Republican lawmakers faced afrom voters upset over some policy changes, chief among them new limits on labor union rights.
In a statement today, Senate Majority Leader Harry Reid praised Kohl and addressed the electoral landscape in Wisconsin. "We know that Wisconsin is dealing with unique challenges today. But Republicans have created an environment in the state where any one of our qualified, Democratic candidates can win," he said.
Added Democratic Senatorial Campaign Committee Chairwoman Sen. Patty Murray, "If there's one place in the country where Republicans have overplayed their hand it's in the state of Wisconsin, and that gives Democrats an even better opening to hold this seat."
Before joining the Senate in 1988, Kohl worked as an investor and founded the Kohl's grocery and department stores. The 76-year-old is also the owner of the Milwaukee Bucks NBA franchise. His personal fortune was a clear advantage in his political career, and Democrats may have to invest more money into Wisconsin in 2012 now that he is retiring.