Democratic presidential candidate, billionaire Tom Steyer speaks during the New Hampshire Democratic Party Convention at the SNHU Arena  on September 7, 2019 in Manchester, New Hampshire.
Columbia, South Carolina CNN  — 

A staffer on Tom Steyer’s presidential campaign in South Carolina resigned late Monday after accessing volunteer data from Kamala Harris’ presidential campaign.

The Steyer campaign announced the resignation of Dwane Sims, the campaign’s deputy South Carolina state director, after initially placing him on administrative leave over the weekend. Sims previously worked for the South Carolina Democratic Party as a voter file manager with access to campaigns’ proprietary data.

In a statement, Steyer’s campaign manager Heather Hargreaves apologized.

“The Steyer campaign takes this issue very seriously. When we first learned about the matter, we conducted an internal investigation and wiped Mr. Sims’ computer to make sure the data was completely deleted and that there was no access to other campaign data. We understand the sensitivity and importance of this information,” she wrote.

“We apologize to the South Carolina Democratic Party and the DNC. Tom Steyer and the Steyer campaign extend our deepest apology to Senator Kamala Harris and her campaign.”

Sims did not respond to a request to comment. The breach of data was first reported by The Post and Courier.

Hargreaves said in an earlier statement that Sims was able to access other presidential campaign data after the South Carolina Democratic Party turned off voter file access to Steyer’s campaign and then reinstated it.

“Within minutes of realizing this, Sims called the South Carolina Democratic Party to alert them, and the access was turned off by the party authorities,” she said.

An official with the Democratic National Committee said Sims exported Harris’ volunteer data, according to an internal user log.

“We take this matter very seriously, and that is why we immediately worked with the DNC to disable this employee’s access to VoteBuilder,” South Carolina Democratic Party Chairman Trav Robertson said in a statement.

“All data downloaded by this individual was destroyed and was not provided to any third parties,” Roberston added.

Steyer said on Twitter he was disappointed and reached out to Harris personally.

“I was deeply disappointed to learn of this situation, and have personally reached out to @KamalaHarris. To every organizer who is putting in the work for a candidate they believe in: I’m grateful for your efforts. Your hard work is what will defeat Donald Trump in 2020,” Steyer tweeted.

Harris campaign aides and supporters voiced outrage over the breach. Harris, who has struggled with low polling number nationally, invested heavily in the Palmetto State to create a robust field organizing footprint.

“Our organizers and volunteers work incredibly hard, and as this story notes, our campaign ‘has built a particularly extensive field organizing operation in South Carolina.’ It’s unfortunate anyone would try to steal that work from our team,” Harris’ national press secretary Ian Sams tweeted.

CNN’s Kyung Lah contributed to this story.