COLUMBIA, S.C. (AP) — Election Day has arrived for the most expensive U.S. House race in South Carolina history as Democratic U.S. Rep. Joe Cunningham tries to hold on to the seat he managed to flip from Republicans in 2018.

Cunningham takes on Republican state Rep. Nancy Mace on Tuesday in the district that stretches from Hilton Head Island to Charleston. He was the first Democrat to flip a U.S. House seat from Republicans in the state since 1986, and national Republicans started targeting his seat just days after his election in the hopes of regaining a majority in the House.

Money has poured into the district: Cunningham has raised $6 million and Mace raised more than $4 million between the Republican primary and the general election. The $10 million total makes it by far the costliest U.S. House race in South Carolina history.

It may be days before all the votes are counted. In Dorchester County, 13,500 mail-in ballots could not be read by scanners because of a printing error. They will need to be entered by hand, and officials would only say they would have that finished by Friday's deadline to certify results.

Mace has focused on partisan politics, saying Democrats across the country don't match the district's values and Cunningham votes with his party most of the time. She calls him “Democrat Joe Cunningham” almost every time she addresses him.

Cunningham is emphasizing his willingness to work with Republicans. His first U.S. House vote was against Nancy Pelosi to keep her job as speaker, and he sided with Republicans against a resolution to limit the president's ability to use military power against Iran earlier this year. Cunningham did vote to impeach President Donald Trump.

Cunningham and his supporters are trying to use his 2018 win to transform the political map of South Carolina. Democrats around Charleston are challenging Republicans up and down the ballot.

Mace was the first woman to graduate from The Citadel and spent two terms in the South Carolina House.

The district along the state's southern coast is richer, more educated and less conservative than much of South Carolina. It also had the smallest gap of any Republican-represented congressional district in the 2016 presidential election, going to the GOP by about 14 percentage points.

___

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

___

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