Judge says Education Dept partisan out-of-office emails violated First Amendment

Is there no federal defamation law that could apply here? I would've thought this would fall under something like that, rather than 1A. Even without 1A, you could still be defaming someone by misrepresenting that they hold a certain view, right? I know states have laws against this regardless of the constitution, but is there no such thing at the federal level?

Only individual people can be defamed, not political parties.

Plus what is being asserted is not really a factual statement so it can't be a lie.

Politicians are allowed to say things like "my opponent believes such and such".