Vice President Kamala Harris’ campaign aims to wrap up her presidential bid by Wednesday nightsecuring a majority of the nearly 4,000 Democratic delegates needed to win the nomination, according to Reuters.

Campaign officials and allies have made hundreds of phone calls to drum up delegate support ahead of the Aug. 19-22 Chicago convention, while also seeking to deflect potential challenges to her.

Locking in delegate support is necessary to ensure that Harris replaces Biden on the Nov. 5 ballot as the party’s nominee against Republican Donald Trump.

Harris needs the support of a simple majority, or about 1,969 of the 3,936 Democratic delegates, to secure her nomination at the August convention. About a quarter have pledged their support so far, based on public announcements.

“Her endorsement from Biden was very powerful in getting donors to give money and delegates to finally commit to her,” Democratic National Finance Committee Chairman Chris Korg, a Florida representative, told Reuters.

The southern US state of Tennessee became the first to pledge its 70 delegates to the vice president, sources told Reuters on Sunday.

Most of the Democratic delegates are committed to Biden after the state primaries. After his announcement that he is leaving the race, they are not bound by any law or party rule to endorse anyone.

The powerful Democratic National Convention rules committee, which is set to meet Wednesday, is planning a mock vote to choose a new nominee before the convention.

Jaime Harrison, DNC chairman, said in a letter to delegates last week that a mock vote would be held between Aug. 1 and Aug. 5 in order to complete the nominating process by Aug. 7, the date Ohio law requires to have one candidate make the state ballot.

Ohio lawmakers then extended the deadline to Sept. 1, but party officials said they hoped to exceed the Aug. 7 deadline to avoid any legal risk in the state.