Liberals have watered down the meaning of Hitler and Nazzism [sic].

Arguably true. Bush was not a NAZI, nor really an authoritarian. Neither one (41 or 43). I didn't agree with a lot of what they were about, but they weren't NAZIs. Cheney was a bit of an authoritarian, and a hawk. I wouldn't say "NAZI".

Trump clearly is an authoritarian. Many people saw the warning signs before the election of 2016. During his presidency, he actually praised Xi for extending his term for "life", and commented that maybe we should do the same (I believe that was 2018). Is he an actual NAZI? Well, he receives support from NAZIs and right-wing nationalists (just look at the Daily Stormer), and he parallels that party leadership from the late '20s both in actions and words (mostly words). He clearly does not respect democracy, is a toxic narcissist, and maybe even a megalomaniac, and foments xenophobia ("blame the other") to whip people up into a frenzy. So you decide if "NAZI" is appropriate.

Whether you use that succinct word or not, he's everything I just outlined in the above paragraph.

But, yes, you do have a point that overusing a word like 'NAZI' can diminish what that truly means. And it also innurs people so that when an actual NAZI shows up, people don't notice.