He's campaigned for other candidates before, and I expect he will do so in IA when the time comes. He's a player. But he isn't running. He has said so again and again.
But go ahead and make trouble where there isn't any. As for me, "Sufficient unto the day is the evil thereof." YMMV.
Campaiging for other candiddates is fine, as long as he isn’t campaigning for candidates like the guy he endorsed in Indiana - Governor Mitch Daniels - the guy who VETOED a state bill which would make Sharia ILLEGAL in Indiana and invited a bunch of Imams to a prayer meeting in the State House (Do I see a Christie pattern of Islamophilia here?)