There aren't many comparable breaches to this one. The closest in modern times may be Hillary Clinton's email server being used for government business. In that case, the FBI investigated and declined to bring charges, under the expectation that a jury would be unlikely to render a guilty verdict.
Okay, fine. But the FBI investigated and laid out the facts.
My fear is that the current administration sees this as a PR problem. No, this was an operational failure. We should feel lucky that merely an American journalist was added by mistake.
We should expect the FBI to investigate this, too. But I worry the facts are too inconvenient for even that level of accountability.