It is estimated that as many as 40 percent of illegal aliens in the U.S. did not illegally cross the border to get there. They are people who came with legal visas and remained after their visas expired. The Department of Homeland Security has specifically identified 1.2 million individuals who are probably in this category, but in 2015 only managed to arrest about 3,400 of them. The government still lacks the means to check the departures of visa holders, even though this has long been promised. Several of the 9/11 terrorists were visa overstay illegal aliens.
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