Former Attorney General Eric Holder and his law firm, Covington & Burling LLP, will conduct vetting of potential running mates for Vice President Kamala Harris’ campaign for the presidency, according to two sources familiar with the matter.

Harris is running for the Democratic presidential nomination after President Joe Biden announced on Sunday he was stepping aside.

A campaign spokesperson for Harris declined to comment.

Holder did not respond to a request for comment.

The selection of a running mate is one of the most important early decisions Harris, who is aiming to wrap up the Democratic nomination in the coming days, can make at the beginning of her campaign.

Biden selected her as his running mate in 2020 and said in his letter on Sunday that it was the best decision he had made.