I am a lawyer, but not a trademark lawyer. Just knowledgeable enough to be dangerously wrong, I guess.

But trademark protection must be tied to a product, and don't provide protection against a word or phrase being used at all.

And so the strength of a trademark description relies on where it lies on the spectrum between totally fanciful words invented specifically for the trademarked use (Xerox, Exxon, Pepsi), arbitrary words that are normal words but have nothing to do with the product (Apple computers, Monster energy drinks), suggestive words that have something to do with the product (Coppertone for suntan lotion, Airbnb for an online service for BnB listings), descriptive words (Quarter Pounder for a burger that is a quarter pound in weight), to fully generic words for products that can't be limited to one producer/seller (bicycle, automobile, hamburger).

Common terms can be trademarked, but the scope of protection is necessarily much narrower. Apple can enforce its trademark in computers and electronics. Monster Energy Drink can enforce its trademark in beverages.

Crowder's "Change my mind" trademark seems pretty tough to enforce. It's at best a descriptive mark, and descriptive marks are hard to enforce unless the mark is so distinctive in commerce (like McDonald's Quarter Pounder) that a consumer might be confused about who is producing it. I don't think any regular person on the street will assume that a CNN-produced town hall with James Talarico is sponsored or licensed or produced by Crowder's team, so there's no risk of consumer confusion.

But like I said, I'm not a trademark lawyer so I wouldn't put too much weight in what I say.

In the end I agree, it can't be enforced, but if it helps:

Trademark protects source indicators, for specific goods and services, so a phrase isn't simply trademarkable or not on its own, it depends on what it is relating to.

There's different levels of protectibility as well - but "generic" is a higher bar. If something is just "descriptive" then it's really just describing the goods or services. Those can't be trademarked unless there is "secondary meaning" which is established consumer association with using that phrase for a good or service. There's also "suggestive" marks, which are less direct than descriptive, "arbitrary" marks which are words applied to unlike goods and services, and "fanciful" (edit: correction) marks which are totally made up words. All that goes in order of protectibility.

Basically, Crowder shouldn't (IMHO) have gotten this mark for debate products/services, because it's descriptive to what debate is. Somehow he did without the USPTO fighting back. Maybe USPTO was overworked and it slipped by.

Ultimately, though, an infringement would only succeed if another party used it in a way that caused confusion over the source/endorsement. Crowder would have to show people saw them say "change my mind" on CNN and thought Crowder was involved. If it was in the title of the show, a huge slim maybe. But in the full show, in a debate, with someone saying "change my mind," it's absurd to think Crowder has a case.