“All of whom” is always correct because of the preposition “of” making it use the object form.

You could drop the “of,” but it changes sentence structure to making “who” be the subject (er, I think) like, “Nearly all who voted did so to overturn the election.”

But “Nearly all of who voted to overturn the election” is wrong because the subject/object is broken.

IMO it’s extraneous for the headline anyway, and should have removed any who/whom, shortening it to, “Nearly all voted to destroy our democracy because they are traitors to the United States and should all be removed from office under the 14th Amendment.”

But eh.

Using the “substitute a pronoun” method:

It’s true that “they tried to overturn the election” would lead to “who”

BUT the whole phrase would be “nearly all of them tried to overturn the election” which leads to “whom”.

So you’re not right, but not crazy to be confused.

It is not. A quick gut check is if you would use “they,” then “who” is appropriate and for “them” use “whom.”

To be a bit more explicit for you, the subject of the verb ‘tried’ is not ‘who(m)’ in this case. It’s ‘all’.