Perhaps Jim Mattis should have stuck it out after all.

Jim Mattis made the judgment that if his commander-in-chief no longer trusted in his advice it was time to go. He resigned hours after Trump's decision to withdraw the 2,000 US troops from Syria. But perhaps he acted prematurely. Honourably no doubt, but if he had stuck it out and continued to argue for a more phased withdrawal, he might have succeeded, making his resignation unnecessary. I know it's easy to say that in hindsight. But Lindsay Graham, that wily old Republican senator and supporter of Trump, went and had lunch with the president at the White House and came away saying Trump wasn't going to bring the troops all out in a one-off withdrawal but would manage it more slowly, only after Isis had finally been totally vanquished in northeast Syria. So Graham got what he wanted. Why didn't Mattis do the same? Why didn't he go to Trump and say: "OK, Mr President, I know what you're saying, and of course it's what you promised in your election campaign, but might I suggest you do it nice and slowly so that we can finish off doing what has to be done?" Trump might have listened. He listened to Graham who was publicly critical of his decision to withdraw the troops. Of course for Mattis the Syria question was not the first moment when he and his commander-in-chief had clashed. It had become a regular occurrence. Nevertheless Mattis's presence at the Pentagon and in the Trump cabinet was too important for him to consider resignation as the only way out. Mattis officially bows out tonight with a phone call handing over the reigns of Pentagon power to his deputy, Patrick Shanahan. I suspect Shanahan will only be the acting defence secretary and won't get the top job. Who knows, perhaps Trump will offer it to Lindsay Graham, and Graham will accept it. He would probably only have to do two years. Either Trump will fail to win a second term, or if he does succeed - beating the likes of Senator Elizabeth Warren who announced her 2020 presidential bid today - he will want a new and fresh cabinet.