Joe Cunningham (copy)

Democratic congressional candidate Joe Cunningham on Monday received the endorsement of three coastal mayors, who all cited his stance on offshore drilling as the basis for their support.

Another wave of coastal South Carolina mayors endorsed Democrat Joe Cunningham on Monday in his congressional run, a sign that offshore drilling is emerging as a defining issue in the race.

The three mayors — Patrick O'Neil of Sullivan's Island, Billy Keyserling of Beaufort and Miriam Green of Awendaw — all cited Cunningham's opposition to offshore drilling and seismic testing as the basis for their support.

"Washington needs to hear from us, not the other way around," O'Neil said in a statement. "One important issue is oil and gas drilling off our shore. As a former ocean engineer, Joe has a deep understanding of how drilling and seismic testing would damage our economy and environment. His pledge to put the Lowcountry over party is a breath of fresh air in today's world of partisan politics." 

The 1st Congressional District race has emerged as the most closely watched in the state because Democrats view it as their best chance to flip a Republican-held seat. 

Even so, it will be an uphill battle: The last time a Democrat represented the seat was nearly 40 years ago.

The latest round of endorsements comes about one month after two Republicans, who are also mayors, pledged to support Cunningham over their own party's GOP candidate, Katie Arrington. Those mayors were Tim Goodwin of Folly Beach and Jimmy Carroll of Isle of Palms.

"We are proud to have the support of so many coastal mayors from both parties who understand the importance of having a congressman who will reject offshore drilling at every step," Cunningham said in a statement from his campaign.

Municipal races in South Carolina tend to be nonpartisan. Both O'Neil and Keyserling told The Post and Courier they identify as independents. Attempts to reach Green about her political leanings were unsuccessful.

Earlier this year, the Trump administration announced plans to open nearly all U.S. coastal areas for offshore oil and gas exploration. Florida's coastline was the only one granted an exception.

Arrington said during a Beaufort League of Women Voters forum earlier this year she supported President Donald Trump lifting the ban on offshore drilling. She later released a statement saying she does not support drilling for oil off the coast of South Carolina.

It was her first public break with the president since she launched her campaign last year.

Keyserling, the Beaufort mayor who has pledged to go to court to stop seismic testing if it moves forward off South Carolina's coastline, cited Cunningham's consistent stance on the issue.

"Now more than ever the Lowcountry needs to speak with one clear voice in our opposition to offshore drilling and seismic testing. Joe Cunningham has been clear from the very beginning that he will oppose any and all efforts to drill and test off of our beautiful coast," Keyserling said.

The endorsements also signal a return to normalcy on the campaign trail after Arrington was critically injured last month in a car accident on Highway 17 South near Adams Run.

Arrington was released from the hospital Friday, where she expressed her desire to resume campaigning in the coastal district, which spans from Hilton Head Island to McClellanville.

A February poll from Winthrop University found a narrow majority of South Carolinians oppose offshore drilling but that the issue is largely geographic. The same poll found 54 percent of residents in the state's coastal communities oppose drilling.

Gov. Henry McMaster became the first and highest ranking state official in the country to back the Trump campaign two years ago but has repeatedly pushed the White House to exempt South Carolina from offshore drilling.

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

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.