Accusing someone of criminal activity is protected speech? The president maybe but a fed governor?

it's opinion based on disclosed facts. opinions, by definition, cannot be defamation

If you say why you're accusing them, definitely yeah. You'd also get into sovereign immunity and FTCA territory (I think?) which makes this a whole lot less likely to succeed.

Yeah. You cannot successfully sue for defamation a federal employee acting in their official capacity.

The press secretary would not be able to exist as a concept if this was not the case