It's a "guidance" or somesuch from like the 60s(?). Idea was it would be unduly burdensome for a president to have to worry about criminal charges: impeachment is how justice is supposed to be achieved with a criminal president.exactly, but it doesn't matter when the crime was committed.
and where does it say they can't be charged? or is it just not worth the effort becasue they may be able to pardon themselves?