It's not because it's "an official act" but because the decision grants total immunity for any actions a president takes using the “core powers” that the Constitution bestows on the office. One such power is the authority to command the military.

Sigh. The positions differ, and I do admit there are Lehal Pros reading it that way. I just agree with Albaby, and before he explained it, that if the act is outside of the scope of his authority (powers) then it isn't an official act except possibly in limited circumstances which I tried to describe. It isn't within Presidential powers to order Seal Team 6 to assassinate a political rival. If you accept that, then that action becomes an unofficial act. I just don't think it was written well, and it appears Sotomayor may have misunderstood it as well, and that goes back to oral arguments. If it isn't reasonably clear, it's a bad decision though.

I don't like the limit on inchoate crimes though. The Constitution spelled it out for Congress, if they had wanted to, they could spell it out for the President. Maybe it was too touchy a subject for three months of wrangling.