Trump's immediate response was to grab the Marine's hat, which he did, and placed it back on the Lance Corporal's head and patted him on the arm.
The hat blew off again and was retrieved by an officer who placed it back on the Marine's head as the President climbed aboard.
It isn't a big thing for someone to do that and help another person out. But it's bigger than it seems. The very human response Trump showed reveals his character. With all the fame and fortune, Trump is still, in many ways, a 'regular guy'. And he's a guy who obviously loves the military.
Compare that to former failed President Obama asking a Marine to hold an umbrella for him and the President of Turkey (Obama called him the "Prime Minister," but CNN didn't report that mistake).
Compare Trump to Obama who can't even properly pronounce "Navy corpsman."
It's no surprise Trump beat the screaming liberal banshee for the presidency.