1986 Amnesty of 3 million illegals, that didn't work well. A sign of insanity is repeating the same thing over again and expecting different results.
Reagan and Bush did what was called "Cleanup EOs" meaning by working with congress they did what they had to do to enforce the laws they signed. But these were flawed laws that didn't take everything into account. Too many ends were not tied up when the bills were signed. So an EO merely facilitated it's enforcement.
Obama isn't working with congress. He's working against them. He is purely lawless, and he has no precedence to site for this action. The only way this would be legal is if it followed the signing of an amnesty bill.