Haven't they caught terrorists at the border?

@ JoeRogan inquires about the number of terrorists entering the United States via the southern border, given the hundreds of thousands of illegal crossings each month and the hundreds of apprehensions from the FBI's terror watchlist?

"One of the things that people are really concerned with is like, what if terrorist cells have gotten in across the border?

When you're letting in hundreds of thousands of people across the border, what are the odds that a few of them are terrorists?

Haven't they caught terrorists at the border? So, how many of them snuck through?"