According to [Fentanyl seizures at US-Mexico border up 750 percent][1]:


>The amount of fentanyl seized by border agents has skyrocketed in recent years, from two pounds in fiscal year 2013 to approximately 1,485 pounds from Oct. 1, 2016, to Sept. 30, 2017  

and according to [Inside a truck in Nebraska, troopers found enough fentanyl to kill millions of people][2] 118 pound of fentanyl is enough to kill 26 million people.  


So enough fentanyl was seized by border agents in FY2017 to kill every American.  As long as 50% makes it through (and 2018 is at least as much as FY2017), the claim is defensible.  


  [1]: https://www.washingtonexaminer.com/news/fentanyl-seizures-at-us-mexico-border-up-750-percent
  [2]: https://www.washingtonpost.com/news/to-your-health/wp/2018/05/25/inside-a-semi-truck-in-nebraska-troopers-found-enough-fentanyl-to-kill-26-million-people/?noredirect=on&utm_term=.9b3042c2e234