Barack Obama s final speech as president was as much a warning as it was a farewell—a warning to Americans that they re still in the middle of crafting their country s history.

Democracies are most vulnerable, the president said, when their citizens forget they re pursuing a common goal.

What he didn t say, but really didn t have to, is that such a unified sense of purpose is currently in short supply.

Quoting George Washington s own farewell speech, Obama said Americans should reject the first dawning of every attempt to alienate any portion of our country from the rest or to enfeeble the sacred ties that make the country one.

When Obama was elected in 2008, social media was still young.

Now it has become the fault line along which political discourse fractures, making the country s commonly held ideals—and commonly enjoyed successes—all too easy to overlook.

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