Data shows that most illicit fentanyl is smuggled into the U.S. through the southern border and, specifically, through Ports of Entry (POEs) and by U.S. citizens.
In 2021, U.S. citizens were 86.3 percent of convicted fentanyl drug traffickers—ten times greater than convictions of illegal immigrants for the same offense.
(that comes from cato, but I’m not linking to a right wing propaganda firm)
Immigration authorities say nearly all of that is smuggled by people who are legally authorized to cross the border