The article explains that a decent legal system is no protection if the social norms that prevent all out political competition are no longer in force. The treatment of Obama represents an example.
An even more basic norm under threat today is the idea of legitimate opposition. In a democracy, partisan rivals must fully accept one another’s right to exist, to compete and to govern. Democrats and Republicans may disagree intensely, but they must view one another as loyal Americans and accept that the other side will occasionally win elections and lead the country. Without such mutual acceptance, democracy is imperiled. Governments throughout history have used the claim that their opponents are disloyal or criminal or a threat to the nation’s way of life to justify acts of authoritarianism."**
read more: Is Donald Trump a Threat to Democracy?