The guy passed background checks to enter the US legally. He passed Uber's background checks and had driven for them for six months - they pulled him from the list after the attack. Either Uber isn't as safe as its proponents claim or no background check can be 100% effective. I guess your answer, unspoken, is no Muslims allowed in ever! What do you do then about people like Paddock in Las Vegas or born in America converts who get radicalised? There is NO easy answer.