Why future presidents will be thankful for Supreme Court ruling in Trump v US

Monday’s Trump v. United States opinion made clear that a president or former president "may not be prosecuted for exercising his core constitutional powers, and he is entitled, at a minimum, to a presumptive immunity from prosecution for all his official acts." 

Chief Justice John Robert’s majority opinion also said that "the President enjoys no immunity for unofficial acts, and not everything the President does is official."

The opinion did not, however, provide precise definitions for what exactly is considered an official or unofficial act, and left that question of fact-finding to the lower courts.