The Bill of Rights is a barricade protecting Americans from their government. Part of President Obama's legacy will be that he inflicted damage on that barricade, eroding freedom of speech, free exercise of religion, the right to bear arms and the right to due process.
Through his political arguments, executive actions and political leadership, Obama has taken some of the holes punched by previous presidents and made them broader or more permanent.
This means that after Obama leaves office, people will be more easily silenced, killed or disarmed by their own government. Obama is leaving behind a public less protected from state power.