If you actually read the Manifesto, you'd know he rants (indeed, possibly in parody) about any number of subjects, including Global Warming (vis-a-vis "Green Nationalism"), etc. Determining he is a "rightwing Trump-supporting extremist" from this is merely a MSM rhetorical flourish.
As is typical in Manifestos, he states his main problem (low white birth rates, ie The Great Replacement), but manages to digressively usurp any number of side issues along the way (see the 8 octants in the title page already). Sort of like the "Green New Deal" lurching all over the place, rather than merely be concerned about the End of the World in 12 years.
You can also see the effect of Big Media: anyone can buy Unabomber Manifesto from Amazon for cheap bucks, while they are trying to hide Tarrant's rantings even on the Internet for some reason?
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