"may be inferred from a firm's possesion of a dominant share of a relevant market that is protected by entry barriers"
Arguably I left out "protected by entry barriers", but that seems obvious for search.
You're splitting hairs over the word popular now.
For example: https://www.documentcloud.org/documents/7273448-DOC.html (page 3)
I'm not saying they are "for sure" a monopoly. I am saying notable numbers of reasonable people with expertise in the space think they are. It's not as clear cut as you're saying.
This entirely new example you are giving is an example of partisan posturing, not evidence of a monopoly. Look at the political affiliation of every single person who signed the letter, and look how many days it was filed before the last federal election.
Again, being popular doesn't make something a monopoly, neither does being a popular target for Republicans.
I didn't say that, though, or anything like that.
I did mention market share dominance. But that's often related to things like "A firm is a monopolist if it can profitably raise prices substantially above the competitive level.".