In an Oval Office meeting with President Trump on Monday, President Nayib Bukele of El Salvador said that he would not return a Maryland man who was wrongly deported from the United States and sent to a notorious Salvadoran prison.

Mr. Bukele, who has positioned himself as a key ally to Mr. Trump, in part by opening his country’s prisons to deportees, sat next to the president and a group of cabinet officials who struck a combative tone over the case, which has reached the Supreme Court.

“Of course I’m not going to do it,” Mr. Bukele said when reporters asked if he was willing to help return the man, Kilmar Armando Abrego Garcia, a 29-year-old father of three who was deported last month. The Trump administration has acknowledged that his deportation was the result of an “administrative error.”

The message from the meeting was clear: Neither Mr. Trump nor Mr. Bukele had any intention of returning Mr. Abrego Garcia, even though the Supreme Court has ruled that he should come back to the United States. The case has come to symbolize Mr. Trump’s defiance of the courts and his willingness to deport people without due process.

Mr. Trump also mused about the possibility of sending American citizens convicted of violent crimes to prison in El Salvador, although he said Attorney General Pam Bondi was still studying the legality of the proposal.

“If it’s a homegrown criminal, I have no problem, no,” Mr. Trump said. “I’m talking about violent people. I’m talking about really bad people.”

Before the full group of reporters was allowed into the Oval Office for the meeting, television cameras captured Mr. Trump telling Mr. Bukele to build more prisons.

Mr. Trump invited some of his top officials to Monday’s meeting, much of which was held in front of news cameras. Ms. Bondi and Stephen Miller, who is the architect of Mr. Trump’s immigration agenda, accused Mr. Abrego Garcia of being a member of the MS-13 gang.

Mr. Abrego Garcia has never been charged with or convicted of being in a gang. In 2011, Mr. Abrego Garcia’s lawyers say, he fled threats and violence in El Salvador and came to the United States illegally to join his brother, a U.S. citizen, in Maryland. He later married an American citizen. In 2019, an immigration judge prohibited the United States from deporting him to El Salvador, saying he might face violence or torture there.

Mr. Abrego Garcia’s lawyers did not immediately respond to requests for comment.

“That’s up to to El Salvador if they want to return him,” Ms. Bondi said. “That’s not up to us.” Mr. Miller went further, arguing that a federal judge had overstepped in directing the administration to provide a road map to Mr. Abrego Garcia’s return. “Neither the secretary of state nor the president could be compelled by anybody to forcibly retrieve a citizen of El Salvador from El Salvador who again is a member of MS-13,” he said.

Mr. Bukele followed suit, saying that returning Mr. Abrego Garcia would be akin to smuggling “a terrorist into the United States.” As the Salvadoran president talked, Mr. Trump, surrounded by cabinet members who spoke in support of the president on cue, smiled in approval.

On Monday evening, more than an hour after the deadline ordered by a judge, the Justice Department submitted its daily update outlining what steps it had taken to return Mr. Abrego Garcia to the United States. It echoed many of the recalcitrant remarks that administration officials had made in the Oval Office.

Representative Hakeem Jeffries of New York, the top House Democrat, called on the courts to hold Trump administration officials in contempt.

“The Supreme Court and/or the federal district court actually needs to enforce its order,” Mr. Jeffries said on MSNBC, suggesting that contempt citations could be directed at the secretaries of state and homeland security, as well as their subordinates.

Mr. Abrego Garcia’s wife, Jennifer Vasquez Sura, said the American and Salvadoran governments were playing “political games” with her husband’s life.

“My heart is heavy, but I hold on to hope and the strength of those around me,” she said.

Stephen Vladeck, a law professor at Georgetown University, said the idea that “the government can disappear people to a foreign country with no due process and no responsibility for what happens next” amounted to “a rule-of-law crisis.”

“If the government can do it to Abrego Garcia, they can do it to anybody,” Mr. Vladeck said.

In Mr. Bukele, Mr. Trump has found a partner in his efforts to force scores of migrants to a Salvadoran prison and keep them there with little regard for checks and balances.

The Supreme Court last week ordered the administration to “facilitate” Mr. Abrego Garcia’s return, but it never defined the specific steps that U.S. officials should take to carry out the plan. Ms. Bondi on Monday argued that the court ruling means the United States would need to help with Mr. Abrego Garcia’s return — such as by providing a plane — only if Mr. Bukele were to decide to send him back to the United States.

“The court gave the administration an opening and the administration has taken a millimeter-wide opening and driven a Mack truck through it,” Mr. Vladeck said.

Michael G. Kozak, the senior bureau official in the State Department’s Bureau of Western Hemisphere Affairs, said in a sworn statement on Saturday that, based on information from the U.S. embassy in San Salvador, Mr. Abrego Garcia is “alive and secure” in the prison known as the Terrorism Confinement Center, or CECOT.

In a legal filing on Sunday, the Justice Department also argued that the courts lacked the ability to dictate steps the White House should take to return Mr. Abrego Garcia because only the president has the power to handle U.S. foreign policy.

The Trump administration has invoked a centuries-old wartime authority to deport migrants to El Salvador by alleging that they are members of violent gangs like MS-13, which originated in the United States and operates in South America, and the Venezuelan criminal group Tren de Aragua.

The law, the Alien Enemies Act of 1798, allows for the summary deportation of people from countries at war with the United States.

While some of the deportees had criminal convictions, court papers have shown that the evidence the government has relied on to label some of them gang members was often little more than tattoos or clothing associated with a criminal organization.

Though the administration resisted helping Mr. Abrego Garcia, Senator Chris Van Hollen, Democrat of Maryland, said on Monday that he wanted to discuss with Mr. Bukele returning the Salvadoran migrant. He added that he would travel to El Salvador this week if Mr. Abrego Garcia was not returned.

The Trump administration doubled down on its incarceration agreement with Mr. Bukele on Sunday when it announced that it had sent 10 more people alleged to be members of the two gangs to El Salvador over the weekend.

Mr. Bukele has found a spot on the global stage through opening the doors of his prison system to Mr. Trump.

The Biden administration treated Mr. Bukele, who has referred to himself as the world’s “coolest dictator,” as a pariah. The Justice Department under the previous administration even accused Mr. Bukele and the Salvadoran government of secretly being lenient toward certain gang leaders. Mr. Trump has appeared to admire Mr. Bukele as a MAGA equivalent in Latin America who won’t hesitate to defend his domestic agenda.

At times on Monday, Mr. Bukele and Mr. Trump broke from discussing immigration to show they were aligned in criticizing politicians who supported allowing transgender athletes to compete in women’s sports.

Mr. Bukele also joked about how his staff does not include “D.E.I. hires.”

Mr. Trump and Mr. Bukele have paired their tough-on-crime personas with highly sensationalized public relations campaigns on social media.

After a surge of gang violence in El Salvador, Mr. Bukele imposed a state of emergency, which has yet to be lifted, and directed the police and military forces to carry out mass arrests. Many of the 85,000 Salvadorans who were arrested disappeared into the prison system without trial and without their families knowing whether they were alive.

“The United States should be holding Bukele’s government accountable for these serious violations, but instead the Trump administration is cozying up to and copying Bukele’s authoritarian playbook — rounding up people with no evidence, denying them any due process and disappearing them in abusive Salvadoran prisons indefinitely,” said Amanda Strayer, the senior counsel for accountability at the advocacy group Human Rights First.

Still, Mr. Bukele’s popularity has soared, and he was re-elected in a landslide last year as his government reported a drop in violent crime. The Trump administration just last week changed a travel advisory for El Salvador, effectively saying it was safer to visit than countries like France or the United Kingdom.

The Trump administration cited El Salvador’s progress in driving down gang violence over the past three years, even though the Justice Department previously accused Mr. Bukele of doling out favors to gang members in exchange for keeping homicide numbers down.

Mr. Bukele described the decision on social media as akin to receiving a “gold star.”