It's a shorthand symbol for the word "and."
I don't mean to be harsh, but no matter how I look at it, I can't help but think 6.000.000 deaths deserve more than a "shorthand symbol".
What kind of a hurry was he, that he couldn't take the time to spell out three letters in memory of a genocide?
Anyways, reading Trump's message, my initial, knee-jerk reaction was to make a sarcastic remark about how I finally facepalmed hard enough to rip my brain out of my skull, and thus was now in the right condition to begin understanding him on a better level.
But thinking about it, I'm actually concerned this poor man might simply be authentically senile.