And that hints at why there is a concept of Presidential Immunity - if in the course of executing duties of the office, such as related to war, a President shouldn't have to worry about getting convicted of murder. (In fact, by legal definition, such actions shouldn't be classified as murder at all).
The legal confusion, which appears to be perpetuated by the "Trump legal team", is that this immunity applies to any action of the President, when very likely it doesn't; if a President goes out and punches a reporter because they get angry, that is not an action related to executing duties of the office, so should have no protection.
Now maybe there are some grey areas; is assassinating the leader of an aggressive militant group reasonable for the security of the nation, or is it just a personal ego trip of the sitting President? But I don't think the "Trump legal team" argues that point, even if they recognize the difference - they want to stretch it to the extreme, not discussing the difference between action against "a political opponent" versus action against "a threat to the nation." Sure someone who is a threat to the nation is also likely a political opponent, but it's not the political opposition that warrants aggressive response.