Old Johno has let it slip that since the government shutdown, lots of people have contacted him urging him to stand for president again.
It is difficult to assess who these people would be, although there is some speculation that it could be family members and friends trying to boost his spirits.
Some of them if they exist at all could be, Hillary Clinton, Nancy Pelosi, Harry Reid, Lindsey Graham, Debbie Wassermann Schultz, and Maxine Waters. The latter two might just be confused enough to think he is a Democrat, although to be fair; quite a few Republicans think the same thing.
On the Tea Party side, it is possible that Rand Paul and Ted Cruz want him in the contest to split the RINO vote in the primaries.
Democrats might be cheered by his entry into the race, owing to the likelihood of a GOP win next time. With McCain in the job, there would be little change from the current situation.