Iowa's 1st congressional district has been run by a Republican lawmaker for the past four years. However, with trouble brewing for the dominant party in the run-up to the 2018 midterm elections, some of the GOP's top donors are quietly dedicating thousands of dollars to prop up the incumbent.

Rep. Rod Blum, R-IA, a member of the conservative House Freedom Caucus, has been courting some of the party's top donors while he lags in the polls behind the favorite to be the Democratic nominee, Abby Finkenauer, a member of the state's House of Representatives, first quarter financial filings show.

Blum has received the financial backing of hedge fund billionaire Robert Mercer, who, through a contribution to the joint fundraising committee Protect the House, gave $5,400. The PAC itself has supported Blum, with $30,000 of its net joint fundraising efforts going toward his cause.

Charles and David Koch are also quietly backing the Blum campaign. The KochPAC, which represents the interests of the billion dollar conglomerate Koch Industries, has ponied up $5,000 for the Republican incumbent so far this year. In 2017 it shelled out a total of $3,000 to back Blum's efforts.

Still, those big names haven't been enough for Blum to overtake Finkenauer in the fundraising game. In total the GOP incumbent raised $303,000 in the quarter while the Democratic candidate brought in $482,000. Meanwhile, the candidates are close to breaking even with the amount of cash they have on hand with the Republican maintaining just over a $1 million and the local state lawmaker holding onto $720,000.

The polls have also not been kind to Blum.

In a district President Donald Trump won by three points over his Democratic opponent Hillary Clinton, Blum's approval ratings have continued to dip. Public Policy Polling recently reported that 54 percent of the district disapproves of the job he's done. He's also lagging behind the president. A poll by Progressive Iowa showed Trump with a 41 percent approval rating while Blum was at 34 percent.

The Republican lawmaker, however, is not phased by his recent polling woes.

"I've never led in a poll paid for by Democrats, so I take those results with a grain of salt." Blum said in a statement to CNBC.

All of those struggles have led the Cook Political Report and Larry Sabato's Crystal Ball, non-partisan newsletters dedicated to tracking campaigns across the United States, to label Iowa's first district as a tossup.

In the meantime, Finkenauer has been getting the blessing of some powerful Democratic groups.

The Democratic Congressional Campaign Committee, the fundraising arm for Democrats who want to run for the House of Representatives, named Finkenauer as one of their "Red to Blue" members.

"Abby, a first-generation college graduate and Iowa State Representative, launched her campaign in April and is a proven advocate for working families," the DCCC website says. It also notes President Barack Obama won the district twice when he ran for office.

Finkenauer has also received the sponsorship of EMILY's List, a political action committee that claims their dedicated to helping Democratic women get into public office.

Her first quarter campaign financial data shows the group has given her just over $15,000 in an effort to flip the seat.

Finkenauer's campaign sees the recent polling data and successful fundraising efforts as the momentum they need going into the June 5th primary and final stretch of the election.

"Abby comes from a labor family and her momentum is a sign of her strong labor roots and commitment to fighting for Iowa's hardworking families," campaign manager Joe Farrell told CNBC.

So far, some marquee Republican fundraising organizations have not financially backed Blum's quest to maintain his presence in Iowa.

The National Republican Congressional Committee, a group dedicated to assisting Republican candidates for the House, has not spent anything to back his campaign, according to the Center for Responsive Politics

A spokeswoman for the committee, however, told CNBC the group would do whatever it takes to help Blum win and that its lack of spending in the area is common practice because it has yet to do so for those not running in special elections.

"We don't discuss spending decisions, but we will do what is needed to ensure Rod Blum is reelected," the spokeswoman said. "We haven't spent yet in any races that are not special elections this cycle. That's common practice," she added.

However, the Congressional Leadership Fund, a super PAC that hopes to defend and maintain the Republican House majority, announced on Tuesday that they will be spending $10 million on digital advertising in races across the country, including in support of Blum.