That’s sorta what I was thinking. He’s self-conscious about his hands, and so probably intentionally makes a loose fist to make them look bigger.
He chose instead to hire sycophants who tell him he looks wonderful.
It’s almost like he’s trying to make a “V for victory” sign, but he doesn’t know how to shape his fingers into a V.
It’s actually kinda in between an A and an S, which is what is wrong with it, if you ask me. An A requires the thumb to be completely to the side of the fingers, and wouldn’t be mistaken for a fist; with the S, the thmb is fully folded over, so it crosses the middle finger and usually most of the ring finger. The S is what you do when you make a fist. You’d break your fingers hitting someone with an A hand, and still not hit very effectively. You want your fist as tight and compact as possible, which Trump doesn’t seem to know.
I suppose he is trying to imitate this gesture?
I mean, he’s not alone. Though Bernie has his more above his head.
ETA: it occurred to me after posting, Trump is holding his little fist at exactly the same level you would if you were doing ASL for “I love you“. I wonder if it’s all lumped together in his head…
If you were to actually hit something with such a fist, there’s a high probability that you’ll jam your thumb, possibly breaking or dislocating it. Martial arts that involve hitting spend a lot of time learning how to make a “proper” fist because it’s insanely easy to hurt your own hand if there’s any sloppiness to your fist.
This is what comes to mind for me: Wallace - That's It! Cheese! - YouTube
I’m sure that he thinks it’s really cool. I’m also sure that normally he bites his lower lip while making that gesture while “dancing”.
As for the white around his eyes, it’s from the tanning bed goggles.
I dunno, I think Bernie’s fist looks a lot different from Trump’s. Bernie’s looks like a “conventional” fist, with all four fingers curled inward and the thumb bent over the pointer finger and middle finger.. With Trump, his pinkie, fourth, and middle finger are curved inward to his palm, but his pointer finger is straighter, giving you a good view of his fingernail. And his thumb only slightly overlaps with the pointer finger.
Although my “natural” fist is not like either one, I find Bernie’s fist easy to replicate. Trump’s is unnatural … I have to consciously set my pointer finger and thumb to match the photo.
Just like that thing on top of his head, the colour of his face, and his grotesquely short fingers.
Which hand are the M&M’s in?
Trump’s fist bugs me.
But what REALLY bugs me about Trump is the way he claps for himself! He shows up for his rallies and the audience of his MAGA-nuts all applaud and cheer. He waves to a few, then he claps along with them!
Crazy!
~VOW
It’s hard to make a proper fist without fully opposable thumbs.
In psychopathology, it should be called the Narcissist Clap. It illustrates the whole reason he has these Nazi-type rallies, which otherwise serve no purpose when he’s not actually campaigning except to feed his insatiable ego. Even Hitler’s rallies, as unhinged as they were, had a definite political purpose. Whereas the Orange Shitstain has no actual politics, no ideology, no moral compass, no values, no soul, and no goals that extend beyond himself and his own self-aggrandizement.
I seriously can’t think of a thing about trump that doesn’t bug, irritate, annoy, etc. etc. me. Every time I have the dis-tasteful surprise of catching his face on a screen, I am sincerely disgusted. When I happen to see his “dance” I have the uncontrollable urge to punch him in his stupid face. Good thing I sit a good 15 feet from the tv. I just have to be careful of my laptop and phone. 
Just like the Soviet leaders used to do
In their case, it’s; “Do this… or else!”
[I apologize if this was already included in any of the earlier links.]
There’s no particular place to hold your hand when you make the ILY handshape. You can make one with each hand and put them together, palms parallel, with a small motion, and it means something like “making out.” You can hold your arm out and sweep the handshape over a crowd to mean “I love all of you!” You can hold it down by your waist, to genuinely, or playfully, conceal it. I could go on and on.
He is kind of holding his hand the way hearing people somewhat new to ASL hold their hands when fingerspelling.
Weirdly, after studying it, it looks like he’s afraid to let his hand get too far away.