Arrington Cunningham composite

Republican Katie Arrington and Democrat Joe Cunningham are both running for office in South Carolina's 1st Congressional District.

With Republicans fighting to maintain their control in Washington and Democrats rallying to unseat them, one of the 2018 midterm races worth watching is right here in South Carolina's 1st Congressional District.

After incumbent U.S. Rep. Mark Sanford was knocked out of the race in the June GOP primary, the seat is now an open one that first-time congressional candidates Republican Katie Arrington and Democrat Joe Cunningham are fighting to win.

Midterm elections by their very nature are a referendum on a sitting president, but findings from the Pew Research Center show it could be even more intense this year.

A higher percentage of voters say President Donald Trump will be a factor — positive or negative — in their 2018 vote than any previous president in any election in the past three decades. The findings also show 34 percent of voters nationwide view their vote for Congress as a vote against Trump, while 26 percent consider their ballot as a vote for the president.

How that breaks here could make all the difference for both candidates in this race.

The district spans much of the South Carolina coastline from Charleston south, with boundaries wrapping around parts of Charleston, Berkeley, Dorchester, Colleton and Beaufort counties linking a conservative mix of retirees, suburbanites and military veterans.

It misses significant Democratic voting blocs, such as North Charleston, that mostly ended up in the 6th Congressional District represented by U.S. Rep. Jim Clyburn, D-Columbia.

In 2016, Trump bested Democratic presidential candidate Hillary Clinton in the district by 13 points. By contrast, the more moderate Mitt Romney outdid President Barack Obama in the district by 18 points.

But Charleston, the most populous county in the district, has shown some movement to the left, morphing in recent years from red to purple in voting preference.

In 2012, about 50 percent of Charleston voters cast a ballot for Democratic President Barack Obama as opposed to the 48 percent who went for Republican Mitt Romney. Democratic support held steady at 50 percent for Hillary Clinton in 2016, but Donald Trump only secured 43 percent.

Other parts of the district, such as Hilton Head and Kiawah islands, have become slightly more centrist, but Democrats have not made significant gains there. Beaufort County, which is heavy with retirees, went for Trump over Clinton by a 55-41 margin in 2016.

Berkeley County was the highest for Trump in the district: 56 percent.

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Democrats point to Trump and a more fractious Republican Party as an opportunity.

Compared with returns in the rest of the state, Trump snagged just 53 percent of the vote in the 1st District.

Meanwhile, Republicans are leaning on history. The last time a Democrat represented Charleston and the Lowcountry in Washington was in 1981.

But nothing is certain.

The nonpartisan Cook Political Report recently moved the race from "likely Republican" to "lean Republican." It shows the outcome is not guaranteed; it will be a fight.

Reach Caitlin Byrd at 843-937-5590 and follow her on Twitter @MaryCaitlinByrd.

Political Reporter

Caitlin Byrd is a political reporter at The Post and Courier and author of the Palmetto Politics newsletter. Before moving to Charleston in 2016, her byline appeared in the Asheville Citizen-Times. To date, Byrd has won 17 awards for her work.