https://ballotpedia.org/State_laws_and_party_rules_on_replacing_a_presidential_nominee,_2020

Democratic Party rules governing vacancies See also: Democratic presidential nomination, 2020 Under Article 2 of The Bylaws of the Democratic Party, the Democratic National Committee (DNC) has the responsibility to fill vacancies in presidential and vice presidential nominations between national conventions.[3]

In the event of a vacancy on the national ticket, the chairperson would call a special meeting. Under Article 2 § 8(d), questions before the DNC, with some exceptions otherwise outlined in the charter and bylaws, are determined by a majority vote of the DNC members who are present and voting by proxy. The bylaws also state that voting to fill a vacancy on the national ticket must proceed in accordance with procedural rules adopted by the Rules and Bylaws Committee and approved by the DNC.[3]