Cronyism, corruption and scandal have swirled around Jacob Zuma since before he became president of South Africa in May 2009, and the muck has only deepened since. On Thursday the country’s highest court ruled that he had violated the Constitution by refusing to pay back millions that the government spent improving his home.

Before that, there were reports that the Guptas, a powerful business family close to Mr. Zuma, had offered to arrange cabinet posts for politicians. And so it goes, prompting the secretary general of the ruling African National Congress to warnthat South Africa is turning into a “mafia state.” Yet the A.N.C. steadfastly continues to declare full confidence in the president.

It is a shame that the A.N.C., the party of Nelson Mandela, is allowing its moral and political authority to be so grievously eroded by Mr. Zuma, instead of bringing his corrupt presidency to an end. But the national executive committee of the A.N.C. — which has dominated South African politics since the end of white minority rule in 1994 — is stacked with allies of the president, and evidently loath to take action against him in an election year.

Yet the need for action becomes more urgent with every new scandal. Mr. Zuma’s predecessor, Thabo Mbeki, fired him as his deputy after Mr. Zuma was implicated in a shady arms deal. Then Mr. Zuma was charged in the rape of a friend’s daughter, and later acquitted. In 2014, an independent inquiry found that Mr. Zuma had the government pay for lavish improvements to his home, but the president refused to refund any of the money, leading to the Constitutional Court ruling on Thursday.

Last December, Mr. Zuma abruptly replaced a respected finance minister with a political hack, leading to a national outcry that forced him to install a more acceptable choice. That scandal took a more serious turn when a government official revealed last month that members of the Gupta family had offered him the finance minister’s job, an offer he said he promptly refused. The Guptas and Mr. Zuma denied the accusations, but the scandal added to fears about the government’s management and further shook investors and credit rating agencies.

In its ruling, the Constitutional Court said that in refusing to pay back the millions spent on his home, Mr. Zuma had “failed to uphold, defend and respect the Constitution as the supreme law of the land.” That has been the story of Mr. Zuma’s leadership. The president of South Africa is elected by Parliament, with is dominated by the A.N.C., so a withdrawal of support by the A.N.C. national executive committee would be tantamount to a demand that Mr. Zuma resign. It’s time.