He knows CNN is a soft target because the station’s been floundering for more than a decade trying to figure itself out.
It’s not truly centrist, but it’s not conservative enough to mean anything to trump and his ilk, but it’s not even scraping the bottom of liberalism like msnbc either.
The network doesn’t have many relevant defenders to a lot of Americans, which means he’ll keep hammering at CNN until it collapses under his threats, or it decides to take a principled stand.