Journalists have incredibly broad protections against getting sued for saying something like that. In general, for public or political figures, they can say whatever they want, in a way they never could against a private citizen, for exactly this reason.

There are fuzzy cases at the edges (like Bob Murray suing John Oliver), but Trump is so clearly a public figure that he can’t sue them for libel without getting laughed out of court. This is why he keeps bitching periodically about the libel laws and how we have to fix them; because they protect people’s right to talk about him and he hates that they can do that and he can’t punish them for it.