When elected, Trump made a big point that his opponent should be investigated and "locked up" over the email controversy. Almost immediately after winning the election, he made tacitly clear he was dropping that as a serious proposal, and to the best of my knowledge he did in fact drop it.
For example I remember him saying something to the effect that it was old news and he wouldn't pursue it, very soon after. I don't recall the DoJ formally being directed/asked to begin an actual investigation or inquiry , although the claim was constantly reused to attack and score points politically and energise his voter base. If the DoJ was at any stage asked to look into it, it's pretty clear by now that they have no interest in taking it further either. Nor do I recall him objecting, or railing against DoJ betrayals, trying to fire anyone in DoJ, or significant action being instigated to force them to investigate/prosecute, for example (as he did with other blocked pledges/issues that mattered to him, such as "Muslim country visitors", Muller inquiry, and the border wall). It really seems as if it's just a rallying cry, of no real interest to him now he has beaten her long ago, but useful to energise and counterattack.
But what about Trump's supporters? They can see these things too. They must have anticipated her arrest and likely trial after such a build-up. They can see she is unarrested. They can see he hasn't made, and never did make, any real effort to get her arrested. They can see he stopped really showing he cared about whether she was arrested long ago (if he ever cared other than as a means to win the election) and that he has no interest whatsoever in having her arrested now or in future. They can see that she is, in effect, already broken as a political contender, and is being left alone in peace, as an individual.
I can think of many things that, if I were a Trump supporter, I might chant. But a broken prominent campaign matter that he's made clear he bailed on directly after winning, and hasn't taken interest in pursuing in the years since? Why does that have any power, in 2019? I would feel that was a memory of betrayal rather that a positive attribute, and prefer to let it slide from memory, maybe chant something related to an area where he did visibly fight for what I'd voted and care about.
So why are his supporters adopting that as a "lead" chant at rallies, and not chanting something else - anything else - to avoid focus on such a visibly broken promise from his past election that is fairly clearly, gone nowhere, going nowhere now, apparently was never seriously intended to go anywhere once it got him elected, and virtually certainly is going nowhere in future even if re-elected?