AND THEN THERE WERE 36…. It’s May, and plenty of congressional primary races are already behind us, so it looked like we may not hear any additional retirement announcements this cycle. At least, that’s what the major parties’ campaign committees were hoping.

It’s why the DCCC was no doubt deeply disappointed to hear about the 36th House incumbent to step down at the end of the year.

Representative David Obey of Wisconsin, chairman of the Appropriations Committee and one of the most powerful and longest-serving Democrats in Congress, announced today that he will not seek re-election and will step down after 41 years.

“There is a time to stay and a time to go. And this is my time to go,” Mr. Obey told reporters and colleagues cramming into the hearing room of the House Appropriations Committee, the panel he has led since January 2007. “I hate to do it. There is so much that needs to be done, but, frankly, I’m bone tired.”

Mr. Obey was bracing for what could have been one of his most competitive re-election contests since first being elected to Congress in 1969.

The congressman insists he wasn’t afraid. “I’ve won 25 elections. Does anybody really think I don’t know how to win another one?” Obey said, eliciting, a wave of applause. “Or, for that matter, has anybody ever seen me walk away from a fight in my life?”

Nevertheless, the fact remains that while his party hoped he’d seek another term, Obey is walking away — and waited until May to make the announcement, forcing Wisconsin Dems to scramble.

Obey had already raised about $1.4 million for his re-election bid, and had hired campaign staff. The leading Republican is Sean Duffy, a district attorney and former reality-television-show personality, who’s raised $500,000 and become one of this year’s Republican Party darlings.

It’s a district that should lean the Democrats’ way — President Obama won the district by 14 points — but thanks to Obey’s late announcement, Republicans have a big head start, and sound confident about their chances. As for the Dems, three state lawmakers — senators Pat Kreitlow and Julie Lassa, and representative Donna Seidel — are reportedly in the mix to succeed Obey.

As of today, Obey is the 17th House Democrat to retire this cycle. There are, meanwhile, 19 House Republicans retiring (20 if you count Florida’s Mario Diaz-Balart, who is retiring from one House seat to run for another).

Dems didn’t want to see any more retirements this year, but given Obey’s influence and the competitive nature of his district, this one hurts a little more than most.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.