Jack Smith’s indictment mixed together conduct, like the sitting President consulting with his AG about suspected voter fraud, that clearly would fall within the scope of immunity, with stuff that was clearly not an official act. I don’t know if he was dumb or arrogant, but it was an insane tactical error.
Official immunity is tough and there’s no clear answer. The old canard that “a prosecutor could indict a ham sandwich” has a lot of truth to it. As between a potentially criminal, but duly elected President, and a potentially corrupt, and unelected prosecutor, which one is the bigger risk? There’s a strong argument that it’s better to have elections be the final backstop rather than the judgment of unelected prosecutors being able to override voters.
One of the problem is the "the DOJ's policy of not prosecuting sitting Presidents", while it's understandable it's definitely not great for the rule of law.
And the other is it took too many years for the whole shit shower to drip down. (Garland appointed Smith in November of 2022, and it took ~10 months for the indictment.)