Truscum have the same mentality as TERs. They do believe that trans women are women and trans men are men, but they deny that non-binary is valid and think that there are lots of fake trans people about. Throw in an insistence that trans people need to be getting medical treatment including surgery (not all binary trans people want all the treatment that can be offered, and some of those that do can’t get it for medical or financial reasons) and you have a very problematic viewpoint.
Some of them even buy into the Ray Blanchard model of homosexual transsexuals (actually heterosexual trans people) and autogynephilia (anything that isn’t attraction to the opposite gender is seen as sexual attraction to the idea of being a woman) which is extremely homophobic and transphobic (as well as biphobic and acephobic, Blanchard is in denial that there are any men or trans women who are either bi/pansexual or asexual, and he says he has the phallometrics to prove it. Pseudoscience ruins the day).
Basically it’s gatekeeping, because if there’s one thing that trans people don’t have enough of, it’s gatekeepers. /s
At best truscum need to be told that it isn’t only about them (quite a few are baby trans who haven’t worked this out yet, and some of them do grow out of it), at worst it’s the assimilationist mentality that trans people need to fit into patriarchal society and those who can’t or won’t are the problem.
Where Caitlyn Jenner is on the scale of truscum, I don’t know, but as she is a Republican my thoughts lean to the really bad end of the spectrum.