The number of successful border crossings doesn't include illegal entries that happened via border checkpoints (people smuggled in via vehicles, for instance) or over sea. That number is not available for 2016, but in previous years it added anywhere from 10 to 20 percent to the total number of illegal entries, according to a 2016 Institute for Defense Analyses report commissioned by the Department of Homeland Security.
It's worth pointing out that at the policy level there's no direct relation between the number of green cards granted and the number of illegal crossings in a given year. Illegal entries don't decrease the number of green cards available, for instance, so while it's undoubtedly frustrating for people waiting on green cards to know that others are simply hopping the border, they're not experiencing any harm as a direct result of it.
Border crossings don't even account for a majority of the people joining the unauthorized population in a given year. In fiscal 2016, for instance, the Department of Homeland Security estimated 628,799 people who had previously entered the country legally overstayed their visa that year. Other groups, such as the Center for Migration Studies, have similarly estimated that visa overstays account for about two-thirds of the total number of people joining the undocumented population in any given year.
“The number attempting to get across the Southern border is probably the lowest it's been since at least the 1970s,” said Robert Warren, a demographer with the Center for Migration Studies. “I'm surprised the [Trump] administration hasn't really focused on overstays. That's where the action is.”
Overall, DHS estimated in the fall that, based on Institute for Defense Analyses numbers, “successful illegal entries fell 91 percent between 2000 and 2016,” although DHS cautions that it's still updating and refining the methodology used to generate that estimate. Those figures largely comport with separate data sets, such as Customs and Border Protection's data on border apprehensions, showing a dramatic decrease in activity at the border over the past decade.
“We cannot allow all of these people to invade our Country,” Trump said on Twitter this past weekend. But the premise behind these words is false. The latest federal data, compiled by President Trump's own Department of Homeland Security, indicates that most immigrants who enter the country do so legally. The number entering illegally, meanwhile, continues to drop precipitously.