Well, if the legislature truly cannot make any statue affecting the President, that has some terrifying implications.
It would mean a President is is legally permitted to ignore laws against raping a child on the sidewalk outside 1600 Pennsylvania avenue Ave then murdering all of Congress by blowing up the Capitol.
Recently, a majority on the Supreme Court has claimed there's immunity for "Official Acts", but hasn't laid out any rule for when an official-looking act is actually an unofficial one... They're basically reserving the right to decide later. (Ex: Officially ordering the US military to kill Congress and Supreme Court Justices.)
Not that I want to give the current one any more evil ideas.