The two young men won power in a landmark election in Senegal, triumphing over the political old guard and giving hope to young people across Africa.

Now a deep crevasse has appeared between them.

One of them is Ousmane Sonko, a popular, charismatic activist who was barred from running for president in 2024 after being convicted of defaming a former government official. His friend Bassirou Diomaye Faye ran instead and won, becoming Senegal’s youngest ever president at 44.

When Mr. Faye became president, he appointed Mr. Sonko as prime minister. Two weeks ago, he fired him after months of infighting.

On Saturday, members of their party will choose their next leader in a test of which man wields more power. Mr. Sonko currently serves as the party’s president, while Mr. Faye holds the title of honorary president.

Mr. Sonko, 51, has accused Mr. Faye, now 46, of sidelining their party and drifting away from campaign promises, such as tackling corruption and taking on the elite. Mr. Faye has said the party was building a cult of personality around Mr. Sonko, its founder, and abandoning its principles.

The two men also disagree on how to manage Senegal’s huge debt, but the fallout between them mostly appears to be centered on who should run in the 2029 presidential election.

Mr. Faye is eligible to run for a second term and appears to have plans to do so. Mr. Sonko says the president promised to step aside so that he could run now that he is eligible to do so. “He told me that if I chose to run, he would gladly serve as my campaign director,” Mr. Sonko said at a news conference this week.

After Mr. Faye fired Mr. Sonko as prime minister, he quickly dissolved the government. Mr. Sonko maneuvered to secure a position as parliamentary speaker on May 26.

Mr. Faye is perhaps more prominent on the international stage, but Mr. Sonko has retained a huge following in Senegal.

Mr. Faye has denied telling Mr. Sonko that he would step aside after his first term. “There was no deal between Ousmane and me,” he said in May on state television.

But this week, Mr. Sonko claimed again that he and Mr. Faye had made a deal, and that senior officials of their party had witnessed the talks.

While the dispute plays out, Senegal is facing severe economic headwinds. When giant offshore oil fields were first discovered here 12 years ago, the country seemed headed for an economic boom.

But a recent government audit revealed that the previous administration had left behind $13 billion in undisclosed state debt, threatening an economic crisis. The International Monetary Fund suspended the release of ⁠a previously agreed $1.8 ​billion loan.

How to handle the debt has emerged as a major sticking point between Mr. Sonko and Mr. Faye.

Mr. Sonko made a name for himself railing against the I.M.F., which he sees as a threat to national sovereignty. He has rejected the terms proposed for an I.M.F. bailout, while Mr. Faye has said he would accept the deal as a last resort.

“If we go this way, accept an I.M.F. deal, we will face consequences,” said Babacar Ndiaye, a political analyst at the West Africa Think Tank. The deal would lead to increased fuel, transport and food prices, he said. “Without I.M.F. support, the country will suffer economically, too.”

For some Senegalese, the allure of both men is quickly fading. Both made grand promises that they would transform the lives of young people in Senegal, a country known as a beacon of stability in West Africa.

Few of those changes have been delivered.

While some items on their populist agenda have been addressed — revoking mining licenses, driving out the French military and seeking transparency on massacres carried out during World War II — many voters say little has been achieved in the two years Mr. Sonko and Mr. Faye have been in power.

Youth employment remains high. Data shows that joblessness rose to 23 percent last year.

If Mr. Sonko wins Saturday’s vote in Parliament, Mr. Faye could find himself expelled from the party. But analysts say Mr. Sonko’s control of the party is not absolute. Out of 20 ministers who were part of the president’s cabinet before the government was dissolved, at least four sided with Mr. Faye.

And while Mr. Sonko pushes for aggressive changes, Mr. Faye has had to face the realities of governing as president.

“You cannot have a prime minister who’s trying to be more powerful than the president,” said Mvemba Dizolele, a senior fellow at the Foreign Policy Institute of the Johns Hopkins School of Advanced International Studies.

“It doesn’t work. No system in the world will tolerate that.”

Babacar Fall contributed reporting.