How can it be libellous for varian and various psychiatrists to express concern about Trump's mental health? The erratic, narcissistic, grandiose behaviour is there for all to see.
Those two young 'fans" of the Trumpster express their opinions, others express theirs. Trump certainly allows himself free reign in the way he describes others, e.g. President Obama, anyone who works for CNN or the BBC, anyone who criticises or questions his comments. If he can do it, surely, so can anyone else.
I've never known psychiatrists to make comments like the ones about Trump about any previous president, even Nixon.