"Don't be a tough guy. Don't be a fool." Does it sound to you like a President writing to another? No. But that's what it is. US President Donald Trump has written a bizarre threatening letter to Turkish President Erdogan. The letter, published by several American media outlets, is shorn of diplomatic niceties and begins with an outright threat. Trump warns Erdogan of destroying Turkey's economy and goading him to strike a 'good deal' over military action against Kurds in Syria. And it ends with a curt "don't be a fool. I will call you later".