The race for Iowa’s Senate seat, the second-most expensive contest in U.S. history, is neck-and-neck and the outcome may decide which party wields more power in Washington after Election Day.

Heated fights are underway for a number of Senate seats this year, and each one is critical for control of the upper chamber of Congress, which signs off on both cabinet nominations and judgeships. The Iowa seat could mean the difference between a Democratic sweep and Republicans retaining a majority.

In Iowa, polls indicate enthusiasm has been building for incumbent GOP Sen. Joni Ernst, a former combat company commander. Her Democratic challenger -- Theresa Greenfield, a real estate developer -- holds a 1.5-point lead after three of the four most recent polls gave Ernst a slight edge, according to an average of polls compiled by RealClear Politics. Greenfield’s advantage was 5 points on Oct. 8.

“Every stop I make, I just feel a huge level of energy and enthusiasm,” Ernst, who's seeking her second term, told Fox News from a Winnebago touring the state. “I really think that momentum is on our side.”

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The importance of the contest is evidenced by the more than $200 million that has poured into the race, trailing only this year’s competition in North Carolina for an all-time record.

But the money isn’t coming from Iowa. It is mostly coming from deep-pocketed donors on the east and west coasts of the country with more than $100 million going into Greenfield’s coffers from ZIP codes in New York and California.

Voters are seeing that New York City and San Francisco are “trying to influence the Iowa election,” Ernst said. “Iowans are telling me they can't be bought.”

Greenfield for Iowa Communications Director Sam Newtown argues that his candidate's grassroots campaign is “the most expansive mobilization effort in Iowa Senate history” and that it hasn’t taken a “single dime from corporate PACs.”

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Both candidates have accused the other of accepting “dark money” and have been the subject of Federal Election Commission complaints. Greenfield has been accused of breaking campaign finance rules three times and flagged by the FEC over illegal contributions. A federal judge, meanwhile, ordered the FEC to take action against a dark money group supporting Ernst.

While accusations of campaign finance irregularities have the potential to influence voters, pocketbook issues and health concerns typically trump such matters.

For Ernst, jobs and the economy are the No. 1 issue on the ballot. Moving the economy ahead "safely and responsibly" is pivotal, especially during the damaging COVID-19 pandemic.

Farmers want to know that the renewable fuel standard program will be protected, she added, and that the U.S. will have strong trade deals to secure their exports. While Midwest farmers have benefited from government assistance, many were hurt by the loss of Chinese markets for their crops after President Trump began a trade war with Beijing.

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Ernst also said Iowans want to know that they are adequately protected, which means “not defunding the police.”  

Greenfield, meanwhile, has said U.S. law enforcement has been built on “systemic racism” while noting that not all police officers are racist. She thinks officers should undergo racial bias and de-escalation training and that chokeholds should be banned. 

The use of neck restraints has come under increasing scrutiny following the death of George Floyd, a Black man being taken into custody by Minneapolis police in late May, and the resulting racial justice protests.

Greenfield, who has railed against the Trump administration's handling of the COVID-19 pandemic, has also stressed the importance of strengthening the Affordable Care Act, known as ObamaCare, by creating a public option to heighten competition and bring down prices.

“Health care is the number one issue on the ballot in November,” Greenfield said at the first debate between the two candidates. “Iowans have preexisting conditions" and they want to keep ObamaCare's protections for such medical issues, she added.

The Trump administration has fought continuously to wipe out ObamaCare, though the president has promised that preexisting conditions would continue to be covered, something that Ernst also supports. How that would happen is unclear, since the administration hasn't introduced a comprehensive health care plan of its own.

After the polls close and as the votes are tallied, Americans sitting at home watching should be mindful of the Iowa map.

The metro areas around Ames, Des Moines and Iowa City are liberal-leaning and the winner may be determined by who fares better in the rural parts of the state, the counties that Ernst says Greenfield has neglected. Results from those areas typically take longer to come in.

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Ernst says she has visited all 99 counties in the state and that her opponent has traveled to fewer than half.

“I think that will matter tremendously,” Ernst said. “We'll see those rural areas put me over that finish line.”