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Republican congressional candidate Katie Arrington turns to former congressman Tommy Hartnett as she expresses gratitude for his work during a 1st Congressional Honorees Banquet at Alhambra Hall in Mount Pleasant on Thursday, August 16, 2018. Lauren Petracca/Staff

A poll Tuesday shows Republican Katie Arrington holds a 7-point lead against Democrat Joe Cunningham in South Carolina's closely watched 1st Congressional District race.

The poll was commissioned by End Citizens United, a campaign finance reform group that has endorsed Cunningham. It was conducted by the Democratic polling firm Public Policy Polling from Aug. 30-31. The margin of error is plus or minus 3.9 percentage points.

Forty-nine percent of the 628 voters said they would vote for Arrington, the one-term Summerville state lawmaker who defeated incumbent U.S. Rep. Mark Sanford in the GOP primary by aligning herself with President Donald Trump.

About 42 percent of voters polled said they would cast their ballots for Cunningham, a West Ashley construction law attorney and former ocean engineer.

Nine percent of respondents said they were undecided.

The findings also show Arrington's staunch support of Trump might not be as powerful of an appeal as it once was.

Voters in the district were evenly split on their opinion, with 48 percent having a favorable view of the president and an equal number having an unfavorable one.

Trump bested Democrat Hillary Clinton by 13 points in 2016 in the congressional district that spans much of the South Carolina coastline.

Nearly half of the survey participants, 44 percent, identified as being Republican, while 27 percent stated they were Democrats and 30 percent identified as independents.

"In a district that Trump won by 13 points, Joe Cunningham and his message of reform has put this race into play," End Citizens United President Tiffany Muller said in a statement.

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Though Arrington was the favorite candidate in the poll, her campaign questioned the source of the survey. The Arrington campaign also declined to share its own internal polls.

"This is obviously a biased poll paid for by a big-money outside group backing Joe Cunningham and D.C. Democrats including Nancy Pelosi and Elizabeth Warren, so take it with an entire shaker of salt," said Arrington's campaign consultant Michael Mulé.

Cunningham's campaign pointed to the poll as a sign that he is closing the gap in a district that last sent a Democrat to Congress in 1981.

"We began this race as a total unknown in a district that Mark Sanford won by 22 points. Since then we've narrowed the race to within 7 points by Labor Day. That's an unbelievable swing," said Cunningham's campaign manager Mariah Hill.

The survey was conducted by phone. Only landline numbers were used.

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.