Although Trump and Haley are the only remaining major candidates left, Ryan Binkley has gotten some attention after the Iowa caucuses due to winning more of the vote than some of the more well-known candidates. He is still winning extremely small portions of the vote, and yet he has remained more persistent than the much bigger candidates. Will he drop out before either Trump or Haley leaves the race? Or will one of them fall first?

Note: If the Supreme Court rules that Trump is ineligible to run, I'll count that as suspending his campaign. A ruling by a lower court wouldn't count, since it could be appealed. 

I would also count it as leaving the race if one of the candidates died.