(If you downvote this, please state your reason, thank you in advance.)

Video link:

Donald Trump endorses Mitt Romney (February 2, 2012)

The David Pakman show: Trump Caught on Video Sexually Assaulting Mitt Romney's Wife? [I don't believe David provided the video link]

The sequence of the event and my interpretations:

So, here is what I saw and interpreted the sequence of the event (as Romney keeps on talking nonsense):

@1:44 At first, Ann Romney's facial expression changes a bit. From the smiling expression

@ 1:46 to a bit surprised or scared or disgusted (I can't tell),

@ 1:47 and changed to maybe a forced grimace(?)

@ 1:50 And then, she looks away from her husband to the general direction of the audience. At the same time, Donald Trump pulls the left of his open suit (he never seems to button his suit) with his left hand. @1:48 -1:49

My interpretation:

1. he used his left hand to pull his suit if Trump's right hand is preoccupied, but it doesn't matter if he habitually pulls his suit using hand from the same hand, as it is usually the case.

2. It looks like Trump is touching Ann Romney during these few seconds. The distance between the two is close enough for that to happen without even noticing, as Donald Trump's right side is directly behind her. When she looks away from her husband and to the general direction of the audience, she might be thinking, "does anyone see what he's doing?"

@ 1:52 When Mitt Romney is forced to pause his speech to allow the audience to applause the fact Mitt Romney had the endorsement of Donald Trump

@ 1:53 Ann Romney gets uncomfortable and squirms a bit and maybe nudges him a bit -- enough to give Trump the signal to cut it out. She also steps a bit away from Donald Trump @1:54. And there seems to be a very short exchange between the two immediately afterward (or maybe they just both opened their mouths a bit) @ 1:54 - 1:56.

And what Trump did after this awkward moment: tying his hands at his back

Watch Donald Trump Endorse Mitt Romney for GOP Presidential Candidate

A different video didn't capture the movement, but it did capture Trump's actions afterwards. Trump ties his hands at the back.

my Interpretation:

I don't know if Ann Romney's rebuff caused him to unconsciously tie his hands at the back as a admission of guilt, or Anna Romney told him to do that (unlikely). Or simply Trump wants to change his stance.

Of course, this is mostly speculation:

We speculate, you decide. (Just kidding. It's a play on Fox News' utterly insincere slogan: We report, you decide)

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sidenote: the reasons that Romney wanted Donald Trump's endorsement in 2012

Regardless of the nature of the incidence, Mitt Romney sought Donald Trump's endorsement in order to get the approval of the tea party movement and the "birther" movement who rally around figures like Donald Trump and Sarah Palin. Also, Romney wants to have a better chance to win Nevada.

source:
https://www.pbs.org/wgbh/frontline/film/divided-states-of-america/#video-2

PBS FRONTLINE | Divided States of America | Part II

The relevant segment of part 2 of this documentary: starting, @ 40:14. especially relevant @ 41:56 - 43:56

By the way, the documentary is also a story how the pervasive conservative propaganda machine has been pulling the Republican politicians (and voters) further and further to the far-right and tearing the country apart.