A couple of hours after President Trump welcomed Turkish President Erdogan to the White House on Tuesday, the visitor's security detail roughed up a group of protestors outside the Turkish ambassador's residence. Eleven were injured, including a DC police officer.

The skirmish was an illuminating microcosm of the thuggish dictatorship Turkey is becoming under Erdogan, who has been putting his foot on the gas as he drives his country toward authoritarian Islamism.

Trump seems to appreciate the importance of the US-Turkey relationship. With nearly 80 million people, Turkey is NATO's largest Muslim-majority member. It allows American forces to be stationed at Incirlik Air Base, 110 miles from the Syrian border. Strategically located at the nexus of Europe and the Middle East, Turkey is a gateway for millions, mostly Muslims, fleeing to Europe either to escape war and persecution or else to seek a better life in freer, more prosperous countries.

During his Tuesday meeting with Trump, Erdogan hailed a "new era" in US-Turkey relations. Trump said the meeting marked "a historical turn of tide" in relations. He has constantly praised Erdogan as an ally in the battle against Islamic extremism.

But Trump must be careful. He to freely heaps praise on foreign tyrants and would-be tyrants with whom he believes he can do business. Last month, when Erdogan lamentably won a referendum that tightened his grip on the levers of the Turkish state, Trump, shockingly, called to congratulate him. No other Western leader did so. Most refused to do so because the result may have involved fraud pushed Turkey considerably further down the road to dictatorship.

Trump tends to view people in zero-sum terms, as either a friend beyond reproach or an enemy with no redeemable qualities. He puts Turkey in the former category, probably because it can help America's fight against Islamic State.

But there are a lot of other thorny issues to sort out. Turkey presses America to stop arming Kurdish fighters in Syria and to extradite a Turkish cleric living in Pennsylvania, whom it says orchestrated a coup attempt last year.

Erdogan who came into office in 2003, garnered praise for economic reforms, more liberal civil liberties, and honest efforts to find peace with the Kurds.

But recently, has moved sharply in the opposite direction, jailing thousands of opponents, and brutally clamping down on civil liberties in a way that makes the behavior of Erdogan's goons in DC look like child's play. Erdogan has also proven an inept steward of Turkey's economy, which is beset by cronyism and mismanagement.

Turkey is too important to abandon diplomatically because of its military potency, location, NATO membership, and potential to check Iran's regional ambitions.

But Trump should make clear to Turkey that Washington disapproves of its current course toward autocracy. Failing to do so would be to abandon America's historic role as champion of democracy and defender of free societies.