Denying them access means they can’t ask him questions or cover the event. And it’s not just press conferences, it’s his rallies, threats on print journalists, censorship of websites.
If only the journalists that corroborate the views of the white house are allowed access or the ability to question him, that is a direct limitation on press freedom. Freedom to agree with the white house or you get the boot is not freedom of expression.
I think you get this.