Maybe The Donald needed a wartime consigliere? Tom Hegan wasn’t cutting it?
On the surface there are at least minor disconnects of message between Trump and Tillerson. My impression has been that Tillerson did a decent job of explaining or getting around the appearance of difference of opinion. I bet Tillerson was deliberately kept out of the loop on NK discussions - IOW, from Trump's point of view, this is not sudden. This has been deliberated carefully.