The clearly expressed will of Congress is that federal employees are not typically to be classed as at-will employees. This current Supreme Court majority explicitly said Congress has the authority to constrain executive branch HR policy. I'm not sure I've read an opinion before where Congress made a black-letter declaration of some policy, and the court overturned it because of the perceived will of the narrow majority of voters for the President, but hey, you do you.

I really don't much care about the underlying principles here. I'm a fan of at-will employment. I generally (though with nothing resembling the fervor of this administration) think that the federal employment rolls are bloated and inefficient. But I also believe what I learned in St. Barnabus Elementary about the separation of powers: Congress makes the laws, the President executes them.