WASHINGTON − President Donald Trump has launched a sweeping crackdown on legal entry into the U.S. through a revived travel ban, as his administration takes dramatic steps to block millions of people from taking up temporary or permanent residency.

Trump's extensive effort to keep visitors from nearly two dozen countries out of the U.S. had led the administration to block most travel from places including Haiti and Somalia, revoke temporary protected immigration status for hundreds of thousands of people from nations trapped in conflict, clamp down on student visas − and all but cease refugee admissions.

An unconventional approach melding immigration reforms and national security policy has resulted in the most dramatic restructuring of admissions policy in a generation, with the second Trump administration taking full advantage of a rare do-over in government.

President Trump bans travel from 12 nations, partially restricts entry from seven others

The Supreme Court in 2018 gave Trump permission to keep out foreign nationals whose presence the administration says would be detrimental to U.S. interests. Trump reinstituted and expanded a program last week that puts full or partial restrictions on travel to America from the citizens of 19 nations, with notable exceptions.