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 
If it were planned, he'd have the right equipment for the job (perhaps a suppressed .308 hunting rifle), have it range zeroed for expected distance and know where the SS shooters were setup.
Why suppress tho? You gotta figure you get one maaaaaaybe 2 shots if at all before you're blown away