WASHINGTON—El Salvador President Nayib Bukele said he doesn’t have the authority to bring back to the U.S. a migrant deported in error to a Salvadoran maximum-security prison, as top Trump administration officials struck a defiant tone in response to a court ruling requiring the U.S. to facilitate the man’s return.The case of Kilmar Abrego Garcia—a man who lived with his family in Maryland and was deported in what the Trump administration acknowledged was an “administrative error”—has become a flashpoint in President Trump’s aggressive approach to mass deportation.