MEXICO CITY — Basilia Castañeda said she was such a fervent believer in Mexico’s president that she founded the first chapter of his political party in her small town and stumped with the president’s son on the campaign trail.

Then, in December, the man she has accused of raping her when she was just 17 was nominated by the president’s party to run for governor of her state, Guerrero.

In statements to prosecutors, Ms. Castañeda and at least one other woman have accused the candidate, Félix Salgado Macedonio, a former senator who is favored to win the election in June, of rape. Local news media have reported that another woman made sexual assault allegations against him in 2007.

One of the criminal investigations is still open, yet Mr. Salgado has enjoyed weeks of public support from President Andrés Manuel López Obrador, who has defended the candidate by calling the accusations politically motivated.

The president’s backing of Mr. Salgado is creating significant cracks inside the governing party, presenting a potential challenge to Mr. López Obrador’s popularity and promised transformation of Mexican society.

Even before Mr. Salgado’s nomination, the president had faced growing criticism that he has overlooked, and at times minimized, the scourge of violence against women.

During a news conference on Tuesday, Mr. López Obrador once again blamed the political opposition for the outcry over Mr. Salgado, claiming that it is “such a shame that the feminist movement is used for other purposes.”

When pressed last month by reporters about Mr. Salgado, Mr. López Obrador snapped. “Ya chole!” he said, meaning “that’s enough.”

When Mr. López Obrador won presidential elections by a landslide in 2018, he promised a “fourth transformation” to create a more egalitarian Mexico, including for women. He painted his presidency as a historic moment that would shape the nation as much as major historical transformations like the war for independence and the Mexican revolution.

But allies worry Mr. López Obrador may actually be missing a transformational moment shaping Mexico’s politics and society: a growing feminist movement that is demanding a serious government response to widespread violence against women.

An average of 11 women are killed each day in Mexico, and some critics have equated the president’s defense of Mr. Salgado — and the party’s willingness to back him in the governor’s race — to the broader disregard that abused women face nationwide.

“If Salgado becomes governor, it legitimizes and normalizes sexual violence against women,” said Paty Olamendi, one of several lawyers representing Ms. Castañeda.

A spokesman for the president declined to comment.

José Luis Gallegos, a lawyer representing Mr. Salgado, declined to comment as well. But in an interview with local media he said that the allegations made by a woman to state prosecutors in 2018 were “totally false” and part of a “dirty war” to prevent his client from running for governor. In a Facebook post from November, Mr. Salgado said that he was “the person most interested in” ensuring that any allegation against him was “exhaustively investigated.”

The controversy has prompted rare dissent within the governing party, as some of the president’s closest allies have demanded that the president drop Mr. Salgado from the ticket, including the party’s secretary general and a senator. The former Mexican ambassador to Washington, a staunch party loyalist, tweeted that “rapists and abusers have no place in society.” Last week the minister of interior described her own experience grappling with sexism during cabinet-level meetings.

In a sign of deepening divisions, the governing party’s election commission said Monday that it would hold an internal poll on who should run on its ticket for governor of Guerrero, but did not bar Mr. Salgado from contesting.

In politics “we still have untouchables, and it just so happens that the untouchables are men,” said Lorena Villavicencio, a congresswoman for Mr. López Obrador’s party, the National Regeneration Movement, known as Morena.

She said her colleagues in the party have urged her to stop being so vocal about the case.

“There is a split” between the party and the women’s movement, Ms. Villavicencio said. “We’re talking about a movement that’s very important, that’s disruptive, that’s transformational.”

When protests swept the capital last year after a rape and two murders of women — including a 7-year-old girl disemboweled and found in a garbage bag — Mr. López Obrador dismissed the demonstrations as part of a political ploy. The president also belittled violence against women by stating — without evidence — that 90 percent of all calls reporting domestic abuse were false.

“I voted for Morena,” said Yolitzin Jaimes, a feminist activist who said she was attacked last month by the president’s supporters after protesting outside of an event where Mr. López Obrador was speaking. “I voted like many women in this country who believed that the transformation of the nation was coming.”

“Not anymore,” Ms. Jaimes said.

Mr. López Obrador’s party, Morena, had made women’s rights a central tenet of the campaign. Party officials promised to create a new pact with Mexicans that scrapped elitism and focused on empowering the marginalized, including women and the poor.

Once he swept the 2018 elections, Mr. López Obrador appointed women to half of his cabinet, including the minister of interior, the second-most-powerful government post.

These were the promises that inspired Ms. Castañeda to open the first Morena branch in San Luis de la Loma, in the state of Guerrero, years before Mr. Salgado became a member of the party, she said. The state, one of the most violent in Mexico, is home to poppy plantations that provide the raw material for heroin. It stretches along the Pacific Coast, and includes resorts like Acapulco.

Ms. Castañeda — who has leveled her allegations against Mr. Salgado publicly, including in a news conference — says she was always interested in politics. In 1998, when she was 17, she says, she traveled with her boyfriend to Acapulco, where they planned to attend a meeting with a rising political star: Mr. Salgado.

At the time, Mr. Salgado and Ms. Castañeda’s boyfriend were members of the Party of the Democratic Revolution. When Ms. Castañeda got lost in the city, she said, she asked a taxi driver to take her to Mr. Salgado’s house, where she hoped to find her boyfriend.

Ms. Castañeda said she was amazed by the splendor in which Mr. Salgado lived. She said he offered to help her get back home.

Instead, Mr. Salgado forced her down onto a couch, she said, and raped her.

“He attacked me like an animal,” Ms. Castañeda said in an interview. “And when he finished, he pulled up his pants, took out a 100 peso bill and threw it in my face.”

Fearing for her life, Ms. Castañeda said she never went to the police. Two years later, as depression seeped in, she said she went to the local prosecutor’s office to file a formal report.

But she said the employee at the office persuaded her to reconsider because Mr. Salgado was too powerful. Ms. Castañeda said she gave up — until last year, when it became apparent that Mr. Salgado would run for governor.

When Mr. Salgado first joined Morena in 2017 and was asked by a newspaper about his past, he laughed it off.

“I have more defects than virtues. I am not running to be a cardinal,” he said. “I am a womanizer, a partygoer, a gambler, a drunkard.”

Then in November of last year, Mexican news outlets reported explosive allegations: An unnamed woman had accused Mr. Salgado in 2018 of assaulting her while she was an employee at La Jornada Guerrero, a newspaper he owned. The woman’s claims are detailed in an investigative file opened by the attorney general of Guerrero that year, a copy of which was obtained by The New York Times.

According to the document, the employee said she was summoned to Mr. Salgado’s house in 2016, and that he gave her a soda that tasted funny. When she woke up, she said her clothes were put on incorrectly and Mr. Salgado was looking down at her.

“Do you feel better now, little girl?” he asked her, according to the documents.

She said she fled, but that Mr. Salgado later lured her back to his house by sending photos of her naked and unconscious that he threatened to disseminate online. When she returned, he attacked her, she said, raping and beating her.

When the woman threatened to go the police, Mr. Salgado laughed and said he was too powerful to take down, according to the investigative file opened by the attorney general’s office.

The state’s attorney general at the time, Xavier Oléa, said in an interview that the woman handed over the photos that Mr. Salgado sent her of the rape, and text messages in which he threatened to kill her if she went to the authorities. Mr. Oléa said he thought there was enough evidence to prosecute.

But Guerrero’s governor told him to drop the case, Mr. Oléa said, repeating an assertion he has made to Mexican media outlets. The governor’s spokesman declined to comment.

“He told me not to go forward with it; otherwise the current president would go for his jugular,” Mr. Oléa said, referring to Mr. López Obrador.

A spokesman for the president declined to comment.

In a news release, the Guerrero Attorney General’s office said the investigation into the woman’s claims was “under revision.” The office said Mr. Oléa was “solely responsible for deciding and coordinating investigations” while he was the state’s top prosecutor.

Ms. Castañeda said she filed her own statement with the Guerrero attorney general’s office in November, shortly before Mr. Salgado was named as the candidate. She said she also filed the accusations with the president’s party, which confirmed receiving them in an internal document obtained by The Times. Ms. Castañeda is being represented by Mr. Oléa, the former attorney general, now in private practice.

Last month, the current attorney general’s office informed Ms. Castañeda that it would not pursue her case because the statute of limitations had passed, according to a letter it sent her viewed by The Times. The attorney general’s office did not respond to requests for comment.

“Many years have passed, but I am here,” Ms. Castañeda said. “The pain is still here.”

Oscar Lopez contributed reporting from Mexico City.