Battle lines were drawn on Monday for South Africa’s ANC as voting began to elect a new leader to succeed President Jacob Zuma as head of a party that has ruled since the end of apartheid but faced scandals and corruption allegations.

The vote is perhaps the most pivotal moment for the ANC since it launched black-majority rule under Nelson Mandela’s leadership 23 years ago. With scandal and graft accusations having tainted Zuma’s presidency, the party is deeply divided.

Whoever emerges at the helm of the African National Congress, a 105-year-old liberation movement that dominates Africa’s most industrialized economy, is likely to become the country’s next president after elections in 2019.

A total of 4,776 delegates began casting their ballots in the early hours of Monday, the ANC said, to select between Deputy President Cyril Ramaphosa and Zuma’s preferred candidate, his ex-wife and former cabinet minister Nkosazana Dlamini-Zuma.

Voting was still going on at 0400 GMT.

“Delegates are very exhausted,” an ANC source, who is a voting delegate, told Reuters. “I don’t know how they will run today’s sessions.”

Ramaphosa and Dlamini-Zuma were the only candidates nominated for the ANC leadership at a conference in Johannesburg on Sunday night.