If you hit Donald Trump with any sniper rifle calibre from 150 m distance ANYWHERE on his body, the man's toast. He's a 80 year old jellybean, held together by his personal BigMac/Adrenochrome mix.
But the dude likely played too much COD or CS and simply got convinced that Trump has too much HP and you need to go for the headshot. Motherfucking 
Pro tip if you try to land a crit be immediately ready for them to go prone to avoid getting rekt by your 420° no scope mlg skillz and aim center mass for a guaranteed pownage.