MEXICO CITY (Reuters) - Tens of thousands of gay rights supporters marched through Mexico City on Saturday with both hope and some nagging doubts about the prospect of a presidential election victory by leftist front-runner Andres Manuel Lopez Obrador next weekend.

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Revelers sporting gaudy outfits and everyday garb waved rainbow flags and the Mexican national colors on the capital’s Paseo de la Reforma boulevard just as Mexico’s soccer team was defeating South Korea 2-1 in the World Cup in Russia.

A Lopez Obrador win on July 1 would be a watershed in Mexican politics, but the electoral marriage of convenience he has forged with a socially conservative party worries some of his liberal backers about his commitment to gay rights.

His National Regeneration Movement (MORENA) is part of a coalition with another smaller leftist party and the religious Social Encounter Party (PES), an anti-abortion group with traditional views about family life.

Eager to avoid tension with conservative backers, Lopez Obrador, or AMLO as he is commonly known, has walked a fine line on gay rights, saying he would hold referendums to decide questions like same-sex marriage.

“MORENA has been very quiet, and actually I’m going to vote for AMLO, but I don’t like that he’s been quiet and wants to put our rights to a plebiscite,” said Diego Posada, a gay 52-year-old decked out in a pearl necklace, a long blue dress, gem-studded glasses and a bright bouquet of flowers on his head.

“Like what’s the big fuss?,” Posada asked.

The PES has softened its tone on lesbian, gay, bisexual and transgender (LGBT) issues in the campaign, but many liberal MORENA supporters express unease about the alliance.

“At the start they say they’re going to help you, but when the time comes, they forget us,” said Mitzariy Bonarroti, a transgender woman, originally from the southern state of Oaxaca.

Temistocles Villanueva, a gay MORENA congressional candidate running in Mexico City, acknowledged that the tie-up bothered some supporters, but said it had also changed the PES.

“The PES has had to moderate its stance during the election campaign because they know they’re with two progressive parties,” the 28-year-old told Reuters. “They yielded to us.”

A 2015 Supreme Court ruling effectively gave the green light to same-sex marriage in Mexico. However, the following year Congress rejected legislation proposed by President Enrique Pena Nieto meant to codify the right nationwide.

Gay marriage is permitted in Mexico City and in several states, but elsewhere the process remains slow and bureaucratic.

The pride march has been staged for 40 years in Mexico City, and Villanueva said there was still work to do to protect the community, pointing to the murder of three gay activists in the troubled southwestern state of Guerrero earlier this month.

Paulina Carrasco Hernandez, 35, a transgender psychologist wearing a rainbow colored t-shirt, said she did not believe any party in Mexico truly represented LGBT people, and only used “wash pink” strategies to court their vote.

Carrasco has not decided who to vote for yet.