When the current President of South Africa, Cyril Ramaphosa, took office in 2018, he issued a State of the Nation address seeking to reassure the country, telling them to leave behind negativity, “because a new dawn is upon us.” It was a momentous promise considering Jacob Zuma’s corruption-riddled presidency which preceded Ramaphosa’s election, and it went a long way toward reestablishing South Africans’ trust in the Presidency. However, since then, Mr. Ramaphosa has had trouble rooting out bad actors in South Africa’s government, as members of his own party have retained their loyalty to Mr. Zuma and his practices of backward dealings.

June 29, however, may mark a turning point for South Africa. Mr. Zuma was sentenced to 15 months in prison in a ruling handed down by South Africa’s Constitutional Court which cannot be appealed. Rather than suffering a direct consequence of his corruption, however, Mr. Zuma was penalized merely for his unwillingness to cooperate with the court in an investigation of his presidency.

On the one hand, this leaves South Africans wondering whether the country’s highest court will be able to prove itself capable of upholding rule of law, even against former Presidents. After all, if nothing else transpires, this sentence of 15 months would fall far short in comparison to the extent of Mr. Zuma’s crimes, which may amount to hundreds of instances of corruption, fraud, and money laundering. On the other hand, it sends an encouraging message that the court is serious enough about accountability to put a former President in prison for merely not cooperating, especially after so many attempts to bring Mr. Zuma to justice have failed.

Though it will have taken years and leave much ground yet to cover, further convictions and sentences could finally prove that Mr. Ramaphosa’s “new dawn” has arrived. In 1995, Nelson Mandela—just a few years out of prison and one year into his term as President of South Africa—spoke at the inauguration of this Constitutional Court, calling on it to stand as a “special institution” to protect the constitution and “ensure the continuity of right and justice.”

Now that court begins on a landmark process to live up to its founding assignment. If it can prove itself, the Constitutional Court would do a great deal to reestablish confidence in South African democracy and send a clear message to those opposing Mr. Ramaphosa’s cleanup efforts that even those in power are not above the law.

Mr. Zuma then may go down as the very antithesis of Mr. Mandela: a few years out of the presidency and one year into his long prison sentence.