So the supreme court already ruled the president cannot be held accountable for anyone they kill.
The vice president becomes the president instantly if the president dies.
What is preventing any vice president from waiting until day 1 of their parties presidency, and then murdering the president? And then instantly pardoning themself?
An official act is defined as a purposefully undefinable and thus uncheckable label the temporarily-illegitimate supreme court can apply to any action without reason or precedent so that donald trump can do whatever he wants.