Peter Hamby: "Democrats of all stripes, including Clinton allies, have predicted for months that the former Secretary of State -- who was campaigning for midterm candidates in Iowa on Wednesday -- will face some kind challenge in the race for the Democratic nomination if she decides to run. The prospect of a Clinton campaign seems more likely with each passing day." "But with the presidential race set to lurch into gear after next week's midterm elections and no clear alternative to Clinton emerging, there are questions about whether she will be the sole candidate on the ballot."