At least 480,000 people overstayed their visas last year, adding to a backlog that’s reached some 5 million total, members of Congress said. But immigration agents launched investigations into just 10,000 of them, or about 0.2 percent, and arrested fewer than 2,000, less than 0.04 percent, saying the others don’t rise to the level of being priority targets.

“We utilize our prioritization scheme along with the resources that we have,” Craig Healy, assistant director for national security investigations at U.S. Immigration and Customs Enforcement, said as he struggled to defend the administration’s meager efforts.