Cyril Ramaphosa ascended to the presidency of South Africa several years ago carrying the excitement and optimism of the country’s rising Black professionals, who saw themselves in him: a measured businessman with intellectual gravitas. He seemed an antidote to the previous administration, which had blasted Black professionals as elitists complicit in the continued white domination of the economy.

But as voters head to the polls on Wednesday for the most consequential election in South Africa since the end of apartheid 30 years ago, Black professionals represent one of the grave threats to the precarious grip on power held by Mr. Ramaphosa and his party, the African National Congress, or A.N.C.

Polls predict that the party will receive below 50 percent of the national vote for the first time since the country’s first democratic election in 1994. And Black professionals could play a significant role in the A.N.C.’s demise.

After defecting from the A.N.C. during the scandal-plagued tenure of Mr. Ramaphosa’s predecessor, Jacob Zuma, many professionals returned to the party in the 2019 election. They believed that Mr. Ramaphosa could clean up corruption and turn around the sluggish economy, according to interviews with political analysts and Black professionals.

The return of these voters to the A.N.C. in the last election helped the party retain a comfortable majority, political analysts say.