Mr. Zuma’s term as the nation’s president ends with national elections scheduled for 2019. But since Mr. Ramaphosa’s victory, there have been rumblings inside the A.N.C. that Mr. Zuma should be compelled to step down sooner and make way for Mr. Ramaphosa, to give the party time to repair its reputation.
“The ruling adds to the cumulative pressure on the A.N.C. leadership to act,” said Somadoda Fikeni, a political analyst. “Heading into the elections in 2019, they can ill afford to have a president fighting for his life, with potentially embarrassing revelations during parliamentary impeachment proceedings, while the A.N.C. is trying to rebrand itself.”
In internal A.N.C. elections this month, Mr. Zuma was rebuked by his own party when it elected Mr. Ramaphosa, who had rallied anti-Zuma forces. Mr. Zuma had strongly backed the losing candidate, Nkosazana Dlamini-Zuma, a veteran politician and his former wife.
Under Mr. Zuma, the once-heroic party of liberation became identified with graft and incompetence. Former core supporters, especially in urban areas, abandoned the A.N.C. last year during local elections as the governing party lost control over most of the nation’s metropolitan areas.
The ruling by the constitutional court revolved around a long-running scandal that had come to symbolize the Zuma administration’s deeply rooted corruption and disregard for South Africa’s democratic institutions: his misuse of public funds for upgrades to his homestead in Nkandla, about 300 miles southeast of Johannesburg.
Last year, the court ruled that Mr. Zuma had violated the Constitution by refusing to pay back some of the money. But his party quickly closed ranks and defeated a motion by opposition lawmakers to impeach him.
In September, opposition parties led by the left-wing Economic Freedom Fighters argued in the Constitutional Court that the A.N.C.-led Parliament had acted unconstitutionally by not investigating Mr. Zuma’s unconstitutional conduct.
Godrich Gardee, the Economic Freedom Fighters’ secretary general, praised the ruling and said his party would press for impeachment proceedings to start immediately after Parliament reconvened next month.
Referring to a ruling party that has so far stood behind its troubled leader, Mr. Gardee said that Mr. Zuma’s fate would be decided by the “voting cattle of the A.N.C.”
Under South Africa’s Constitution, the president can be removed by a vote of at least two-thirds of Parliament. The A.N.C. holds more than 60 percent of parliamentary seats, enough to shield Mr. Zuma as long as it remains unified.
But A.N.C. lawmakers now face a more complicated situation. In responding to the court ruling, the party must show a commitment to clean government, but doing so could tarnish the party’s image further if Mr. Zuma and others were forced to testify during impeachment proceedings.
The A.N.C.’s deputy secretary general, Jessie Duarte, said in a short statement that the party would discuss the ruling’s “full implications” at a meeting of its national executive committee on Jan. 10. Mr. Zuma did not comment.
Despite the victory of anti-Zuma forces in party elections this month, Mr. Zuma has shown no sign that he is willing to cede the presidency before his term expires.
In a separate case this month, the nation’s High Court rejected Mr. Zuma’s attempts to block an inquiry into accusations of influence-peddling in his administration. Last year, the nation’s former public protector released a 350-page report on corruption under Mr. Zuma and called for the creation of a public inquiry — a demand Mr. Zuma rejected.
The High Court ordered Mr. Zuma to set up the inquiry within 30 days. The A.N.C., in keeping with its efforts to reshape its image, welcomed the ruling. But Mr. Zuma quietly moved to appeal, in a fresh sign that his interests and the party’s are diverging.
During his two terms in office, Mr. Zuma has been dogged by a series of scandals and legal challenges to his personal conduct. Political analysts have pointed out that one of the reasons he strongly supported his former wife in the recent party election was the hope that a future government led by her could help protect him against further prosecution.