DES MOINES, Iowa (AP) — Six years after Iowa voters overwhelmingly elected her to the U.S. Senate, Republican Joni Ernst faces a tough challenge from Democrat Theresa Greenfield in a race that has been one of the most expensive in the nation.

The two candidates had more than $170 million for spending on media as parties and interest groups poured money into the race, which was eyed as a key battleground for control of the Senate.

Ernst breezed into office in 2014 with an 8-point victory thanks in part to an image molded by television ads of her riding a motorcycle, shooting a handgun and promising to make big-spenders in Washington “squeal.” The squeal ad in particular vaulted Ernst to national attention, as she walked through a barn while noting she “grew up castrating hogs on an Iowa farm” and was ready to cut pork. The ad was interspersed with scenes of pigs and the sounds of squeals.

Ernst’s overwhelming victory, coupled with President Donald Trump’s 9-point win in 2016, left some wondering if Iowa had left behind its battleground status to become a more reliably conservative state.

But polls show support for Trump has declined significantly, and after six years in office and a prominent leadership role aside Senate Majority Leader Mitch McConnell, Ernst has seemed vulnerable to Greenfield’s claims that she has worked more for wealthy lobbyists and corporations than Iowans.

“Sen. Ernst sold out Iowans for her big corporate donors,” Greenfield said in one of three televised Senate debates.

Greenfield has called for a more effective response to the coronavirus pandemic, emphasized health care and her support for expanding the Affordable Care Act and promised to protect Social Security benefits.

Ernst has responded by pointing to her support of tax cuts proposed by Trump and argued she's willing to work with Democrats on issues such as infrastructure. She also has portrayed Greenfield as being controlled by liberal Democratic leaders and eager to push a radical agenda on issues such as taxes and environmental policy.

“What we can’t do is turn our country over to the radical left, those that are funding Ms. Greenfield’s campaign, their extreme abortionist ideas, the radical environmental ideas that would kill Iowa’s farms and eliminate our manufacturing jobs,” Ernst said.

Ernst, 50, served in the Iowa Army National Guard for 22 years before retiring in 2015 as a lieutenant colonel. She also was twice elected auditor of Montgomery County in western Iowa and served in the state Legislature before her election to the U.S. Senate. She’s from Red Oak.

Greenfield, 56, grew up on a farm in southern Minnesota and now lives in Des Moines, where she is president of a Des Moines real estate and development company.

Most polls have shown the race is within the margin of error after months of campaigning and an overwhelming number of television and online ads.

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Find AP’s full election coverage at APNews.com/Election2020.

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Mitch McConnell's title has been corrected to Senate Majority Leader instead of Senate President.