Story highlights Democratic Sen. Tom Harkin attacked GOP hopeful Joni Ernst last week

Ernst called his comments offensive in an interview with Fox News on Monday

Ernst is locked in one of the most competitive Senate races this year in Iowa

A poll released Monday showed Ernst and Democratic challenger Bruce Braley tied

After Sen. Tom Harkin likened her to Taylor Swift, Republican Senate candidate Joni Ernst is taking the pop star's advice.

Just "shake it off."

That's how Ernst responded Monday to Harkin's remarks last week that Ernst wasn't fit to be Iowa's senator just because she's "really attractive and she sounds nice."

"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 at the Story County Democrats' annual fall barbecue, according to footage obtained by Buzzfeed News published Sunday night.

He backtracked on Monday, calling his comments a mistake and praising Ernst's campaign.

"I shouldn't have said those things, I know that. I regret anytime someone feels offended by what I have said," Harkin said. "But I am only human and I can make mistakes sometimes in how I say something. In fact, I have complimented her on running a very good campaign."

His apology came after Ernst fired back Monday on Fox News and in an interview with CNN affiliate KCCI and said Harkin would have never made those comments if she were a man.

"I was very offended that Sen. Harkin would say that. I think it's unfortunate that he and many of their party believe you can't be a real woman if you're conservative and you're female," Ernst said on Fox News. "I believe if my name had been John Ernst attached to my resume, Sen. Harkin would not have said those things."

Ernst also slammed Democrats for their "phony war on women."

"I am a woman and second I have been to war. I am a combat veteran, this is not a war on women and anytime Democrats use the word war, they need to do it to honor our servicemen and women," Ernst said Monday.

Ernst has gained momentum recently in the race against her Democratic opponent Rep. Bruce Braley, leading by two points in the latest CNN/ORC poll and up by 7 points in a Des Moines Register poll released this weekend.

But a Quinnipiac University poll released Monday, one day before voters head to the voting booth said the race is all tied up with each candidate pulling 47%.

Iowa is arguably one of the most crucial Senate races of the cycle that could hand over control of the Senate to Republicans if Ernst prevails.

Ernst would be the state's first female Senator.

Harkin's office did not immediately responded to CNN request for comment Monday.