If Thomas Matthew Crooks had not decided to use a bottom of the line AR-15 with iron sights and splurged on a proper target rifle in a long-range caliber like .300 winchester magnum or 6.5mm Creedmoor and a decent scope. Along with match grade JHP boat tail ammunition, he wouldn't even NEED to know what ranges he is shooting. At the distance he was from Trump he would not have needed to adjust much for windage or bullet drop. He could have aimed for the chest and fired, and maybe even gotten a follow-up shot to the chest again (little chance in surviving that) and there would be no more Trump. The Secret Service sniper would still have blown Crooks's head off, but he would have died knowing he accomplished his goal.