The program's defenders claim that the "lottery winners" who get into the United States via the diversity visa program are vetted as stringently as anyone else. But is anyone really vetted all that stringently at all?
Obviously you can't predict the future, and anyone can surprise you, but the whole point of the travel bans Derrick Watson keeps halting is that we're trying to find a more effective way to do the vetting. Maybe if we can figure that our, we won't keep letting the likes of Sayfullo Saipov into the country: