ANKARA (NYTIMES) - He has already met the Mexican and Chinese presidents and hosted a conclave of 68 nations fighting the Islamic State in Iraq and Syria (ISIS), but no meeting in Rex Tillerson's brief tenure as Secretary of State will be as delicate as the one in Ankara on Thursday with Turkey's president, Recep Tayyip Erdogan.
Erdogan is the leader of an important NATO ally and is crucial in the fight against the Islamic State, but he is also a prickly strongman whose campaign to change Turkey's Constitution in a referendum has many worried that the country is on the precipice of authoritarianism.
The referendum has resulted in the worst divide between Europe and Turkey in decades, with Erdogan accusing European leaders of Nazi-like tendencies after they refused to allow officials of his government to address pro-referendum rallies.
Erdogan also has serious reservations about the American plan to attack the Syrian city of Raqqa, the declared capital of ISIS, and has demanded that the United States extradite a Pennsylvania cleric who the government says was the mastermind behind a failed coup attempt in July.
Navigating these difficulties would test the most seasoned of diplomats. Tillerson, though, has had a rocky start. On a recent trip to Asia, he stumbled repeatedly - disputing a South Korean explanation for his dinner plans and allowing China to crow over his use of language that US diplomats had long eschewed.
Tillerson's aides insist that he is still finding his footing in a complicated job.
But experts in the region say there is no room for mistakes in his discussions on Thursday (March 30) evening with Erdogan.
"It's hard to think of a more important or more challenging relationship," said Antony J. Blinken, a former deputy secretary of state who visited Turkey three times last year to keep the relationship from foundering.
Turkish officials, who have been waging a campaign against Kurdish militants inside Turkey, have repeatedly said they would not accept US plans to use a force that combines both Arab and Kurdish forces to attack Raqqa, since they view the Kurdish units as terrorists.
US officials have repeatedly responded that the combined force is the only viable option.
Overcoming this disagreement is essential since Turkey could derail the fight against the Islamic State in profound ways. Much of the air campaign is being conducted out of Turkey's Incirlik Air Base, and closing the base to coalition bombers, as some Turkish officials have threatened, would be a huge blow.
Turkey has also threatened to send its military against Kurdish forces, a move that would lead to a severe breakdown in the coalition and stall the Raqqa campaign.
Just as important was a series of disasters visited upon Turkey over the past year.
The attempted coup on July 15 killed 290 people and traumatized Turkish politics. Erdogan responded with mass arrests, purges of civil servants and the referendum, planned for April 16, that, if passed, would give him nearly dictatorial powers.
The country also experienced terrorist attacks that cost hundreds of lives and crippled its tourism industry. The economy, after growing smartly for much of the past decade, has been hobbled.
Hammering out a workable agreement with the Turks under such difficult conditions would require intense work and close planning across several US government agencies, said Ryan C. Crocker, a former ambassador to six Muslim-dominated countries.
"And if that's happening on our side, I haven't seen any signs of it," he said.
Turkish officials initially welcomed the election of President Donald Trump, despite his repeated vilification of Muslims, in hopes he would reset relations.
Michael T. Flynn, Trump's first national security adviser, was paid more than US$500,000 (S$698,100) last year by a firm whose Turkish-American owner has links to the leadership in Ankara. But Flynn was fired, and the Trump administration so far has not moved to extradite the cleric, Fethullah Gulen, an ally of Erdogan's before the two had a falling out.
Nothing is likely to be decided about the Raqqa campaign until after the referendum. By then, Erdogan may be loath to alienate the Americans "now that the relationship with Europe is at an all-time low and there are increasing signs that the relationship with Russia is becoming counterproductive," said Sinan Ulgen, a former Turkish diplomat and a visiting scholar at Carnegie Europe.