In an extraordinary letter sent to Turkish President Recep Tayyip Erdogan last week, President Donald Trump warned that he could destroy Turkey's economy if the situation in Syria is not contained and resolved in a humane way, CNN has confirmed.

The tone of the letter is consistent with Trump's unconventional approach to diplomacy, particularly when dealing with strongman leaders, as he tells Erdogan: "Let's work out a good deal" and "Don't be a fool!"
But it's striking to see a US President use such language. Trump also warned his Turkish counterpart not to "be a tough guy!"