MEXICO CITY (AP) — Mexican President Andrés Manuel López Obrador’s governing Morena party decided Sunday that a series of five polls over the summer will decide the party’s nomination for the June 2024 presidential election.

All of the four Morena contenders will have to resign their government posts by Friday, including Mexico City Mayor Claudia Sheinbaum, who is considered the frontrunner. That is meant to prevent primary candidates from using their posts to gain an unfair advantage. Each can campaign throughout the summer.

The party is desperate to avoid splits and accusations of manipulated polls that have marked past primary races in Morena. The four contenders joined hands and chanted “Unity! Unity! Unity!” after the announcement.

Mexico’s top diplomat, Marcelo Ebrard, has already said he will resign this week. Rounding out the field is Sen. Ricardo Monreal and Interior Secretary Adán López, who is no relation to the president.

Two allied parties, the Green and Labor parties, will also field one primary candidate apiece for the coalition's nomination.

Morena has risen to national domination quickly following López Obrador's election in 2018. He cannot run again, and has said he will retire completely from politics after his term ends in September 2024.

But the Morena party revolves largely around the president's personal popularity, and López Obrador has not managed to forge it into a cohesive force. Some members come from smaller left-leaning parties and some from the old ruling Institutional Revolutionary Party, the PRI.

Contenders have cast doubt on the results of internal party polls in past primary races held by Morena. In a bid to avoid such disputes, the party itself will conduct one poll, and each of the four Morena contenders will name private polling firms to carry out four more polls. Each will have equal weight.

There will be no debates between the primary candidates, nor will governors, mayors, Cabinet members or the president be allowed to endorse a candidate during the primary.

The polling will be carried out nationwide between late August and early September. The winner will be announced Sept. 6. Any Mexican — not just Morena members — could be surveyed in the polls.

While the party says López Obrador will not decide the nominee, the president's preference — and any indication of it, however slight — would be determinative.