“We must undertake a rigorous review of our visa and refugee vetting programs to increase our confidence in the entry decisions we make for visitors and immigrants to the United States,” he said. “We cannot risk the prospect of malevolent actors using our immigration system to take American lives.”

Altogether, the United Nations referred more than 100,000 refugees from around the globe last year for resettlement in the United States. The Obama administration accepted nearly 85,000 of them in the 2016 fiscal year, before raising the ceiling considerably for 2017. Now Mr. Trump’s order will effectively leave tens of thousands of families in limbo, all vying for the sliver of seats still available.

Veronica and her sister — whose last names are being withheld to protect their identities — have been waiting to find out whether they will be among the chosen. They and their father have been interviewed a total of four times, but months have passed.

Members of El Salvador’s most notorious gang, MS-13, have made menacing phone calls suggesting that more killings are coming, the family says. So the girls, their father, aunts and uncles abandoned their houses and ran. But in a country the size of Massachusetts, there are only so many places to hide. They have already moved twice.

Officials and immigrant advocates in Central America fear that as the Trump administration cites the danger of admitting potential terrorists cloaked as refugees from nations like Syria, it is disregarding the tens of thousands of people here who are being terrorized by street gangs that actually originated in the United States.

In 2014, the Obama administration began setting up a program to offer refugee status or special entry for some Central American children, hoping to stanch the tide of minors making the dangerous journey to the United States on their own.