While Mr. Trump highlights the construction of a border wall to stress his war on illegal immigration, it is through policy changes, not physical barriers, that his administration has been able to seal the United States. Two more measures were to take effect by Monday, an expansion of his travel ban and strict wealth tests on green card applicants.

“He’s really ticking off all the boxes. It’s kind of amazing,” said Sarah Pierce, a policy analyst with the Migration Policy Institute, a nonpartisan research group. “In an administration that’s been perceived to be haphazard, on immigration they’ve been extremely consistent and barreling forward.”

The number of people who obtained lawful permanent residence, besides refugees who entered the United States in previous years, declined to 940,877 in the 2018 fiscal year from 1,063,289 in the 2016 fiscal year, according to an analysis of government data by the National Foundation for American Policy. Four years ago, legal immigration was at its highest level since 2006, when 1,266,129 people obtained lawful permanent residence in the United States.