However, a major source of illegal immigration often overlooked by many lawmakers and the media alike is foreigners in the United States with some form of temporary legal status overstaying their visas.
Estimates of the total number of illegal aliens living in the United States range from 11-20 million people. While figures vary, it's estimated that nearly half of the illegal population are visa overstays.
USA Today reported on recently released figures from the Department of Homeland Security showing the number of visa overstays in 2017:
More than 600,000 foreign travelers who legally entered the United States in 2017 overstayed their visas and remained in the country by the end of the year, according to Department of Homeland Security data released Tuesday.
President Donald Trump has urged Congress to complete a biometric entry-exit tracking system that would better monitor foreigners who legally visit the United States. Completion of that system, which uses fingerprints and iris scans to more accurately capture when people enter and exit the country, was included in an executive order he signed shortly after being sworn in as president.