MEXICO CITY — El Salvador’s populist president was poised on Monday to claim a resounding victory in the country’s legislative elections, dealing a crushing blow to establishment parties and granting the young leader, who has been accused of authoritarian tendencies, a powerful new mandate.
When President Nayib Bukele, 39, swept to power in 2019, he vowed to overhaul Salvadoran politics. In Sunday’s elections, he appeared to do just that.
Mr. Bukele’s party, Nuevas Ideas — New Ideas — perhaps with the help of a political ally, appeared on track to achieve a supermajority in the Legislative Assembly: 56 of 84 seats.
“Let’s think about what we have achieved,” Mr. Bukele told his supporters on Twitter early Monday. “We are writing the history of our country.”
The vote cements Mr. Bukele’s hold on El Salvador’s politics and endows his party with sweeping powers to replace his staunchest adversaries, including the attorney general, and appoint new members to the Supreme Court. And with Congress and the judiciary stacked with allies, Mr. Bukele could change the Constitution and possibly transform the government in his image.
“There’s no checks on his power,” said David Holiday, regional manager for Central America at the Open Society Foundation. “The people have given him a kind of blank check to kind of rebuild El Salvador in the way that he sees fit.”
The strong showing for Nuevas Ideas came despite allegations of voting fraud from Mr. Bukele and other party members.
In a move that could have come straight from the playbook of former President Donald J. Trump, to whom Mr. Bukele has been compared, the Salvadoran president called a news conference Sunday, as voting was going on, to claim irregularities in the vote and attack the country’s Supreme Electoral Tribunal, the news media and the attorney general.
The president complained that polling centers had opened late and that his party had been denied credentials to observe the vote. He also claimed that some people had been illegally prohibited from casting a ballot, without offering any evidence.
At the news conference, Mr. Bukele encouraged voters to cast their ballots for Nuevas Ideas, appearing to ignore Salvadoran election law, which prohibits campaigning in the three days before polling.
The country’s Electoral Tribunal said it would open an investigation into Mr. Bukele’s comments. It did acknowledge lapses in awarding credentials to officials from the president’s party, but it said the local authorities were free to allow them into voting stations.
On Sunday, the top American diplomat in El Salvador warned against making baseless claims of irregularities in the electoral process.
“It is very important not to say that there is fraud where there is no fraud,” Brendan O’Brien, the acting head of the United States Embassy in San Salvador, said in an interview with Salvadoran media. “It is important to wait for the results.”
The comments from Mr. O’Brien, who took up his charge the day of Mr. Biden’s inauguration, may presage a tense relationship with the new administration in Washington. Veering from the approach taken by its predecessor toward authoritarian-leaning governments, the Biden administration might try to exert its considerable influence to curb Mr. Bukele’s tendencies.
“I expect them to be very tough,” said Mr. Holiday of the Open Society Foundation. He added that he expected the Biden administration to work on elevating civil society voices and “legitimating actors that the government itself doesn’t want to legitimate.”
For voters in El Salvador, Mr. Bukele’s frequent flirtations with autocracy appeared to matter little: In the end, the president’s promise of a brighter future for the country coupled with a slick communication strategy prevailed.
“I voted for Nuevas Ideas because from the get-go I saw Bukele work, that promises are kept,” said Domingo Pineda, 29, a merchant in Santa Tecla, a municipality just outside the capital, San Salvador. “This is a government that is working for the people, by the people.”
Oscar Lopez reported from Mexico City. Natalie Kitroeff contributed reporting from Mexico City and Nelson Rentería Meza contributed from Santa Tecla, El Salvador.