I believe they can step in, but I don't think they will until presented with a "case". Perhaps a denial of venue change etc will get a motion to dismiss where it needs to go.
Can you imagine it? A lowly county prosecutor bringing charges against an ex president? What a liberty! ---Here is something of note--- Purportedly, Trump was trying to cheat the entire state out of their honest result, yet no other county's prosecutors joined in with Willis and her Fani.
What makes the charge idiotic is President Donald Trump had no way to overturn the results. Now, if he ordered the National Guard to seize the ballots, that would have been a basis for charging him. He did no such thing or even interfered in the counting of the ballots. Asking to investigate possible election fraud is not against the law. A number of US citizens tried to challenge it in US courts but, when the US courts turn a blind eye to fraud, there is not much you can do about it.