Have seen multiple interviews this week. Would love for him to run for President. Bright, strategic, honorably has served his country, pure leader. It won't happen, but would he get some major support as a third party candidate?
He'd probably lock the Democratic nominee for the win. You'd get a lot of folks who voted for Trump to vote for him and split Trumps vote. You would not get any liberal voters and few Dems in my opinion. I'm still hoping Trump will make a huge gaf in the coming months giving another decent Repub a chance but the time it takes to get on the ballot etc is running short.
Remember when Trump fired him, he accused Mattis of being more a Democrat than a republican. It really makes not difference to me whether he's more a Republican or Democrat. Either way he is a great & dedicated representative of our military & nation.
Just as an aside I really think the only reason Trump picked him for Sect. of Dehense was his nick name. Which is about as much reflection as Trump is capable of on any appointment