I’m not sure why you think it’s a problem.
A president as verbally incontinent, and as totally unmoored from reality, as Trump is will inevitably, from time to time, come out with things that even his most toadying lickspittles cannot bring themselves to pretend are not batshit insane. In such a case the president needs an off-ramp, and it’s the “Ha ha! That was a joke!” routine.
We know it was not a joke. He knows — in so far as he knows anything at all — that we know that it was not a joke. The toadying lickspittles have an opportunity to prove their spinelessness by pretending to beleve that it was a joke. We know that this is a pretence. They know that we know that it is a pretence.
Everybody — except possibly the president — understands the position perfectly well. Nobody is misled. So where’s the problem?
Sure, it’s dishonest and humiliating for the president, and the fact that the president and everyone around him is indifferent to honesty and positively embraces humiliation is a problem, but there are much, much more worrying manifestations of that problem that this “it’s a joke!” routine.
Obligatory Blackadder quote:
Blackadder: Dr. Johnson left in the highest of spirits, sir. He is utterly thrilled at your promise to patronise his Dictionary.
Prince George: I told him to sod off, didn’t I?
Blackadder: Yes, sir, but that was a joke…surely.
Prince George: Was it?
Blackadder: Certainly! and a brilliant one once more.
Prince George: (happy at the idea he managed to pull off a joke, pretends that it was
his intention all along) Yes, yes! I…er…suppose it was, rather,
wasn’t it…
Blackadder: So may I deliver your note of patronage to Dr. Johnson as promised?
Prince George: Well, of course. If that’s what I promised, then that’s what I must do.
…and I remember promising it distinctly.