October 31.
That’s the deadline to be included on the Florida primary ballot. (Some people are saying Utah and/or Michigan are earlier, but not according to my information.) South Carolina is due the next day.
Once you start missing ballot access, the road gets a LOT harder. If you’re going to run, why put yourself in a hole?
The DNC side is different, though. So much weight is placed on the “super-delegates” that you could miss some primaries and still be well in the running.
Some Info I’ve seen/found:
Utah:
Becoming a Federal Candidate
Office : President
Filing Dates : Between between July 1 of the year before the primary election will be held and 5 p.m. on January 15 of the year in which the primary election will be held
http://elections.utah.gov/register/becoming-a-federal-candidate
Others:
Oct. 31, Florida
Nov. 1, South Carolina
Now. 18, New Hampshire.
Then there is the 3rd party crap and going to a vote in the House.
http://www.freerepublic.com/focus/bloggers/2786040/posts