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."

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