The default mode of employment for the US, except Montana, is "at will."

That means you can be let go, at any time, for any reason, including a bad, unfair, unjust, or inaccurate reason. You can be fired for no reason. Unless you have an actual employment contract stating your employment is NOT at will, you are, by default, at will.

You cannot be let go for a handful of reasons: a protected trait (like your race or religion) or engaging in a protected activity (like making an OSHA complaint or taking FMLA). THAT is "wrongful termination."

But outside that very small list of reasons, it's legal to cut you loose for anything else. Bad, stupid, unfair, or otherwise. And it's not illegal to immediately hire your replacement.