At a moment when many of his former voters believe that America is facing a genuine democratic crisis, former President Barack Obama has been largely silent about what is happening in American politics. Other than a handful of appearances—an interview with David Letterman in a new Netflix show, or an oral history project at MIT—he insists on following protocol and tradition for former presidents, resisting the temptation to jump back into the political fray.

For the past year, President Trump has worked with the Republican Congress to dismantle crucial parts of Obama’s legacy, including affordable health care, progressive taxation, climate-change regulation, oversight of the financial system, and immigration reform. Discussions of Medicare and Medicaid cuts surfacing in recent weeks suggest that an effort to roll back Lyndon Johnson’s Great Society might be next.

That, in itself, is not unusual—when control of the White House switches hands, presidents often work to reverse key policies. And, for the most part, ex-presidents hold their peace, placing the need for a smooth transfer of power and the health of democracy ahead of securing their own legacy.

But what Trump has done over the past 14 months is anything but usual. He has employed recklessly bellicose rhetoric against dangerous adversaries such North Korea, created massive conflicts of interest by refusing to separate himself from his business empire, risked setting off a debilitating trade war without any careful deliberation, generally ignored overwhelming evidence that the Russians tampered and plan to continue tampering in our elections, and has been willing to play in the sandbox with noxious white nationalism. Trump has used his Twitter account, press conferences, and speeches to sow doubts about the legitimacy of the press, U.S. intelligence agencies, and law-enforcement officials. He has brought a level of instability and chaos to American government that is extraordinarily harmful to the health of the body politic.

But Obama has largely remained silent. That should not come as surprise. His reticence reflects one of the problems that constrained his presidency—his hesitation and resistance to getting down and dirty in the muck of partisan politics. He aimed high, but American politics went low.  ...