A front view of Nigeria s opposition party (Peoples Democratic Party) is seen at the Central Area, Abuja before its National Convetion in Abuja, Nigeria on May 28 2022. AFP
The PDP and Buhari's ruling All Progressives Congress party (APC) were both scheduled this weekend to select candidates for the presidency of Africa's most populous country.
But a day before its primaries were to start, the APC announced that it had pushed its party convention back a week to June 6 through June 8.
PDP delegates and political leaders packed out an Abuja national arena, decked out in the opposition party's red, white and green colours, where they voted late Saturday for its challenger for next year's election.
Among the top opposition candidates for the ticket are long-time challenger Atiku Abubakar, former senate president Bukola Saraki and Aminu Tambuwal, the Sokoto State governor who enjoys strong support in mostly Muslim northern Nigeria.
Another hopeful is Rivers State Governor Ezenwo Nyesom Wike, the only main opposition candidate from the south of the country.
"What is the problem of Nigeria? Leadership," Wike told the crowds as aspirants gave their speeches. "I will win... for the power to come back to PDP."
Buhari, 79, leaves after two terms in office, with Nigeria still struggling to end a more than decade-long jihadist conflict in its northeast and a wave of violent banditry in its northwest.
Africa's largest economy is also still recovering from the impact of the coronavirus pandemic and fallout from the Ukraine war that has pushed up fuel and food prices across the continent.
The PDP ruled Nigeria for a decade and a half before its then-president Goodluck Jonathan was ousted by the APC alliance in 2015 to bring Buhari to power.
The APC said the delaying of its own primaries decision followed a ruling by electoral authorities to extend the deadline for the submission of candidates' names.
The APC gave no further details, but the ruling party has been caught in fierce wrangling over who should run, with former Lagos governor Bola Tinubu and current vice president Yemi Osinbajo among the possibles.
Buhari has not endorsed any candidate to succeed him and some analysts expect him to attempt to find a consensus nominee to keep the APC's factions together ahead of the February 2023 presidential and parliamentary elections.
An alliance of smaller parties drawn together for Buhari's 2015 election win, the APC has often struggled to contain internal divisions.
"It clearly means the APC is going the consensus route, which requires more backroom dealing than the usual primaries," SBM Intelligence analyst Tunde Ajileye said of the ruling party delay.
"It also means the consensus candidate is one that many are not accepting easily."
Local media has been discussing a possible return by former president Goodluck Jonathan as an APC candidate after a group of supporters bought him a nomination form. Jonathan himself denied any part in the move.
Under an informal agreement among the political elite, Nigeria's presidency is usually alternatively "zoned" between candidates from the north and the south.
After eight years under northerner Buhari, most agree the presidency should now go to a candidate from the south.
Rotating power at the national government level has been seen as a balancing force in a country almost equally divided between the mostly Christian south and predominantly Muslim north.
Most top PDP candidates like Abubakar are from the north though Rivers State governor is from the south.
Most APC top candidates, including Tinubu and Osinbajo, are also from the south of Nigeria. Former president Jonathan is a southerner.
Since its return to civilian rule from a military dictatorship in 1999, Nigeria has held six national elections, which were often marred by fraud, technical difficulties, violence and legal challenges.
In 2019, when Buhari was re-elected, the Independent National Electoral Commission was criticised for delaying the initial vote by a week. Abubakar, who lost to Buhari, challenged the results in court.