Obama found out he couldn't accomplish his radical agenda constitutionally.  So he proceeded to, even by his own prior constitutional professorial opinions, govern constitutional boundaries.  He attempted to use the Presidency as a dictatorship, issuing decrees making law instead of executing the law and working with Congress to create new law.

BUT, the American system strikes back...for Presidential Decrees expire with the President.  So all Trump needs to do to erase the Obamanation's Legacy is ... repeal his exec orders one by one.  Of course, the lasting damage to the constitutional order is done, that will be Obama's true legacy...that and the damage done by admitting hordes of illegals by ignoring his job as the chief executor of the laws.