I agree with the "who?", but then I'm not big in to TV and film.
The "who cares?" though is particularly problematic - it shows a rise in the normalisation of open threats of violence. Today, it's a political figure who by the definition of the US's party system is going to be a polarising figure - but tomorrow it can be any person that isn't flavour of the week, justified or not.
I was reading the “who cares” as “who cares what he has to say?” (being a furtherance of wondering why this person has a platform or is getting a headline) I read it that way rather than “who cares that someone is threatening to kill the President.” (Which I think how you took it)