There’s no law against hating the President. Find proof it affected their work and maybe you have a reason to fire them . Do it wrong and they sue and walk away with millions.
Especially when they are mostly lawyers and know where the lines are drawn.
Everyone knows there was political bias, but they were smart enough to make it difficult if not impossible to prove it affected their work. It’s like racism - if I don’t want to rent my apartment to a black person I’d never say that was the reason, instead I’d find something like their credit history to use as the reason. They may think it was illegal racial discrimination but they’d never be able to prove it.