David Bellamy became an amiable populariser of science, but at least you initially got the feeling that he was a real scientist - until he starting sounding off about the spurious nature of global warming claims etc. He seems to have held (holds) such views with a degree of vehemence, and claimed that such a stance soon reduced his public popularity and scientific credibility. In fact, he said his career was ruined because of it.
It doesn't take long to discover that much of the 'scientific' data on which he based his views was a load of bollocks perpetrated by known fraudsters, and he was prone to blithely quoting exaggerated data based on nothing more than unchecked typos.
If a supposedly trained scientist can take such a cavalier approach to scientific truth, what hope is there for Donald Trump?