The race in Wisconsin's 7th district is beginning to take shape in the absence of Rep. David Obey (D).

This week Democrats picked state Sen. Julie Lassa to run in place of Obey, and Republican Sean Duffy went up with his first TV ad of the campaign.

Duffy told The Ballot Box he was surprised by the 20-year incumbent's retirement announcement May 5. Duffy got the news when a reporter called and asked him to comment. "I thought it was a prank," he said.

He was putting together a strong campaign and was recently classified as a "Young Gun" by the National Republican Congressional Committee. "Could that have played a factor [in Obey's decision]? Of course," Duffy said. "Did it? I don't know."

Duffy has said it's unclear how Obey's departure will change the dynamics of the race.

"I'm not running against a 40-year incumbent anymore, but my message hasn't changed," he said. "We've been talking about what's wrong with Washington, D.C., what's wrong with the direction the country's going.

"And before we were including Dave Obey in that conversation, but the bottom line: The problems are still there."

The district, which went for President Barack Obama by 14 points in 2008, will still be difficult for a Republican to capture. "I know that," said Duffy. "We're not letting up."

Duffy's first ad was produced by D.C.-based Craft Media Digital and is airing on cable and broadcast television.