The National Republican Congressional Committee is taking aim at longtime Rep. Collin Peterson (D-Minn.) with an ad arguing he has "changed."

"Peterson's always called himself a fiscal conservative, but something's happened," says the ad's narrator. "Collin Peterson's changed. Peterson voted against the budget to cut spending and bring down the deficit, and Peterson voted to keep President Obama's takeover of healthcare, including his half-a-trillion-dollar cut to Medicare. Collin Peterson: He's changed. He's on their side."

The ad buy is small but not insignificant: a bit more than $40,000, which will buy a week of television in the inexpensive Fargo, N.D., media market.

Peterson, now in his 11th term, has faced no serious challenges in more than a decade to his hold on a Republican-leaning northwest Minnesota district, although Republicans have periodically tried to target him.

But Republicans feel good about the chances of Minnesota state Sen. Gretchen Hoffman (R), who announced her campaign in late February. Tea Party-backed Lee Byberg (R), whom Peterson beat by 17 percentage points in the 2010 GOP wave election, is also running.

The Hill rates the race as likely Democratic.

Watch the ad: