(WASHINGTON) — A staffer on 2020 candidate Tom Steyer’s campaign downloaded volunteer data that belonged to fellow presidential hopeful California Sen. Kamala Harris’ South Carolina campaign operation, according to the Democratic National Committee, which issued a cease and desist letter for breach of access Monday night.The Steyer campaign staffer was identified as Dwane Sims by both the Steyer campaign and Democratic National Committee to ABC News. Steyer’s campaign said Sims accidentally downloaded Harris’ files thinking they belonged to their own campaign. He then alerted the DNC that he had access to the data, a spokesperson on the Steyer campaign said.However, call information and logs of when the files were downloaded obtained by ABC News show Sims phoned the DNC at 2:56 p.m. on Friday for a 12-minute call, but the data wasn’t downloaded until 3 p.m. — during the call, not prior to it.The logs also show that “Harris” is written prominently on the files, making it clear the information belonged to that campaign.Sims was placed on administrative leave from the campaign over the weekend, per senior Steyer aides, and the state party banned him from the voter file and all party systems.Then, as news broke of the breach Monday night, the Steyer campaign announced that Sims had resigned.”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,” campaign manager Heather Hargreaves said in a statement.”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,” she added.Steyer echoed this apology in a tweet soon after, and said he had reached out personally to Harris.”I was deeply disappointed to learn of this situation and have personally reached out to @KamalaHarris,” he wrote. “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.”ABC News has reached out to Sims for comment.The Charleston Post and Courier was first to report the incident.Prior to joining the Steyer campaign, Sims worked as the Voter File Manager at the South Carolina Democratic Party.According to the state party, after leaving his post, Sims “maintained a separate user account, which is in clear violation of the VoteBuilder protocol.” VoteBuilder is a software used by Democratic campaigns to combine data and reach voters.The Harris campaign, in response, lauded its own work in South Carolina.“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,” said Ian Sams, Harris’ national press secretary.Copyright © 2019, ABC Audio. All rights reserved.