In an immigration system mottled with escape hatches and hobbled by scant resources, Juan, who fled Colombia six years ago, is one of nearly a million people who have managed to linger in the United States despite having been ordered out of the country by an immigration judge — some of them more than a decade ago.

And with the Trump administration intent on sweeping perhaps millions of immigrants without legal status out of the country, the White House has not had to look far to make a quick mark. Because people with deportation orders have had their day in court, most of them can be sent out of the country without seeing a judge, sometimes within hours of being arrested…

But the follow-up will be complicated. The backlog of what the government calls “fugitive aliens” has persisted through Republican and Democratic administrations, inflamed conservatives who oppose illegal immigration, and resisted the immigration authorities’ attempts at enforcement.

Since 2006, even as the overall total of unauthorized immigrants in the United States has dipped, the number facing outstanding deportation orders has grown by more than half, to around 962,000 people from 632,726. More than half of them come from Mexico, El Salvador, Guatemala or Honduras. (Another 13,200 or so, as of early February, were already in the custody of customs officials.)