COLUMBIA, S.C. (AP) — Before Democratic U.S. Rep. Joe Cunningham was even sworn into office, Republicans vowed to win back the seat they lost in reliably red South Carolina in 2018.

Two years and millions of dollars later, Cunningham is working hard to hold on to his seat in the district that stretches from Hilton Head Island to Charleston.

Cunningham faces Republican South Carolina Rep. Nancy Mace, who calls him “Democrat Joe Cunningham” almost every time she addresses him.

With national Republicans targeting his seat in the hopes of regaining a majority in the House, money has poured into the district.

Cunningham has raised $6 million. Between the Republican primary and the general election, Mace raised more than $4 million, making it by far the costliest U.S. House race in South Carolina history.

Cunningham is emphasizing his willingness to work with Republicans while not forgetting the power he has to help Democrats as the author of the biggest political upset in South Carolina this century.

“While you may not have been with me on every vote, know that I’ve always tried to do the right thing, the right way,” Cunningham says in an ad he shares with his 2-year-old son Boone that started airing the final week of the campaign.

Mace's strategy has been to remind voters in this district that gave President Donald Trump a 14 percentage point win in 2016 that Cunningham is in the same party as House Speaker Nancy Pelosi.

Despite a few maverick votes — like not supporting Pelosi for speaker and going against House Democrats' attempt to limit the president's military power against Iran earlier this year — Mace said Cunningham is a reliable Democratic vote.

“He's just another clone of Nancy Pelosi. That's why I mention her same so much,” Mace said at the end of a debate in October.

Cunningham’s 2018 win was the first time South Carolina Democrats had flipped a U.S. House seat from Republicans since 1986.

Cunningham's Republican opponent two years ago opened a path for the Democrat by beating incumbent Mark Sanford in the primary. Cunningham then cultivated Republicans who were uneasy about President Donald Trump and his stance at the time that the state’s coastline be opened to offshore drilling.

Those Republicans have shown no outward signs of abandoning their new Democratic ally. And Cunningham and his supporters are trying to use his win to start to change the political map of South Carolina. Democrats around Charleston are challenging Republicans up and down the ballot.

The Republican Charleston County sheriff has a competitive race for the first time in about three decades. Democrats are trying to flip four Republican-held state Senate seats in the area.

Mace, the first woman to graduate from The Citadel military college, spent the final weeks of the campaign courting voters at the other end of the district by suggesting Cunningham made a mistake supporting a military budget bill — as did several of the state’s Republican representatives — that required the Parris Island Marine recruit training base to be able to train men and women together in five years.

A Marine leader said closing Parris Island and building a new base somewhere else was one of several ideas being considered, and Mace pounced on the statement with commercials and relentless reminders during debates.

But Cunningham responded by pointing out Republicans like U.S. Sen. Lindsey Graham promised the base would not close. Republican Gov. Henry McMaster promised the Marines they would do whatever was asked of the state to keep Parris Island open.

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Follow Jeffrey Collins on Twitter at https://twitter.com/JSCollinsAP.