Turkey’s President Recep Tayyip Erdogan is a powerful, even at times capricious, leader on a par with the US and Russian presidents, Donald Trump and Vladimir Putin. All three are risk-takers, which means when they come up against each other, the outcome is very far from predictable.

For better or worse, Erdogan has transformed Turkey into a self-confident and assertive power at the key land and maritime crossroads between Asia and Europe. He has very consciously fostered the country’s Ottoman past, in which strong sultans created a major empire whose frontiers once reached even to the gates of Vienna.

For years, successive occupants of the Oval Office in Washington have taken Turkish membership of NATO almost for granted. US military bases and listening posts monitored the old Soviet Union. American arms manufacturers earned good profits as they equipped the powerful Turkish armed forces. They enjoyed a virtual monopoly that even produced a behind-the-scenes row when the defense ministry in Ankara decided to buy some British Land Rovers rather than the US equivalent.

For his part, Putin has transformed Russia, restoring the confidence and national pride that had rusted and decayed so very visibly during the lackluster Yeltsin years. The Russian president is in many ways emulating the autocratic czars and styling himself as a strong and unflinching leader, a type that still appeals to many ordinary Russians.

Thus Erdogan and Putin share many values. And these have brought about a remarkable new relationship between them that has even seen a NATO member buying ground-to-air missiles from Moscow rather than Washington.

The Obama administration answered the challenges from Russia and increasingly Turkey with the po-faced, more-in-sorrow-than-anger style responses traditional to US diplomacy. But in President Trump, Putin and Erdogan face a leader every bit as mercurial and probably even less predictable than they. The State Department wiseacres in Foggy Bottom must be wringing their hands in horror at the once unthinkable but now growing possibility that Turkey could break with NATO and form a strategic partnership with Russia. Such a realignment would very probably transform the geopolitics, not just of the Middle East but also of southeast Europe.

But Trump shows every inclination to play hardball with an increasingly difficult Erdogan, whose assault on America’s Kurdish allies in Syria undermines the Washington-led drive against Daesh (the self-proclaimed IS) in the country. Worse, Turkey is threatening to attack Iraqi Kurds in and around Mount Sinjar, which is also still home to thousands of Yazidi refugees.

However, the straw that has broken the camel’s back is the continued detention of a US pastor, Andrew Brunson, seized in 2016 from his home in Izmir where he has lived for 23 years. He is accused of supporting Kurdish PKK terrorists and the outlawed movement of Fethullah Gulen. Two other Americans who still hold Turkish citizenship are also being held as terrorist suspects.

Even if there is any truth in the allegations, Trump has demanded Brunson be released. And for once, many legislators on Capitol Hill are right behind the president and insist that the charges against Brunson are cooked-up and absurd. And the mood in Washington has not been helped by Erdogan’s developing ties with Iran’s ayatollahs. Therefore, this looks like a serious row that is only just beginning.