MIAMI — About 600,000 Venezuelans and more than 230,000 Salvadorans already living in the United States can legally remain another 18 months, the Department of Homeland Security said Friday, barely a week before President-elect Donald Trump takes office with promises of hardline immigration policies.

Biden’s administration has strongly supported Temporary Protected Status, which he has broadly expanded to cover about 1 million people. TPS faces an uncertain future under Trump, who tried…