Senate Republican candidate Joni Ernst told Fox News on Monday she was "greatly offended" after retiring Sen. Tom Harkin -- the Iowa Democrat she's hoping to replace -- suggested her looks are a factor in her surging campaign.

“I think it’s unfortunate that [Harkin] and many of their party believe that you can’t be a real woman if you’re conservative and if you’re female,” Ernst said. “Again, I am greatly offended about that.”

Harkin, at a local Democratic event last week, said: “In this Senate race, I’ve been watching some of these ads. And there’s sort of this sense that, ‘Well, I hear so much about Joni Ernst. She is really attractive, and she sounds nice.’”

Harkin then compared the candidate to singer Taylor Swift.

“I don’t care if she’s as good looking as Taylor Swift or as nice as Mr. Rogers, but if she votes like Michele Bachmann, she’s wrong for the state of Iowa,” Harkin said.

Though Harkin spoke at a Democratic barbecue last week, his comments gained traction after BuzzFeed posted a video of it Sunday night.

Ernst is running against Democratic Rep. Bruce Braley for Harkin’s old seat. The race is seen as one of this year’s key Senate contests that could determine which party has control of the chamber.

One poll over the weekend showed Ernst up by 7 points, but a new survey released Monday by Quinnipiac University showed them tied at 47 percent each.