Sen. Tom HarkinThomas (Tom) Richard HarkinWisconsin lawmaker gets buzz-cut after vowing not to cut hair until sign language bill passed Democratic debates kick off Iowa summer sprint Key endorsements: A who's who in early states MORE (D-Iowa) said Monday that he “regrets” saying that Republican Senate candidate Joni Ernst was “as good looking as Taylor Swift.”

“I shouldn’t have said those things, I know that,” Harkin told BuzzFeed News, which broke the news of his comments on Sunday. “I regret anytime someone feels offended by what I have 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.”

Harkin drew criticism after comparing Ernst to the music star during an event last week.

“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 BachmannMichele Marie BachmannKlobuchar urges CNN town hall audience: 'That's when you guys are supposed to cheer, OK?' Michele Bachmann praises Trump: Americans will 'never see a more godly, biblical president' Will Biden lead a 'return to normalcy' in 2020? MORE, she’s wrong for the state of Iowa,” the veteran lawmaker said.

Ernst said earlier Monday that she was “very offended” by the comments. But she also found some campaign-trail levity in the situation.

“We're gonna shake this off,” she said, making reference to one of Swift’s most recent singles, entitled Shake It Off.

Swift’s newest album was released a week ago, to significant commercial success.

The race between Ernst and Rep. Bruce BraleyBruce Lowell Braley2020 caucuses pose biggest challenge yet for Iowa's top pollster OPINION | Tax reform, not Trump-McConnell feuds, will make 2018 a win for GOP Ten years later, House Dems reunite and look forward MORE (D-Iowa) has been one of the most closely watched in the country — and remains tight in its final stretch. Both are hoping to replace Harkin, who is retiring at the end of this term.

The conservative Ernst has run an aggressive campaign, bolstered by her background in the military and Braley’s unforced errors.

She successfully made an issue of comments made by Braley appeared to be suggesting that Sen. Chuck GrassleyCharles (Chuck) Ernest GrassleyTrump's latest plan to boost ethanol miffs both corn groups and the fossil fuel industry Syria furor underscores Trump's isolation GOP braces for impeachment brawl MORE was not qualified to chair the Senate judiciary committee because he is a farmer, not a lawyer. Farming is a part of the culture in Iowa, and the attacks stuck.

If elected, she would be Iowa's first female senator.