Leif, since you first brought this up, Wed. afternoon, I tossed this question to the other mods.
The overall impression is that it would not work very well.
Unlike illegal immigration, which was one single topic, threads on specific candidates would have a major problem with staying on topic. It would be darn near irresistible for some to begin comparing one candidates stance on any one issue with another's.
Each thread would, by definition, contain multiple topics as the individual stances are discussed. That would result in multiple conversations going on at the same time.
Given the penchant of a lot of people to not read the entire thread before commenting, can you see where the thread would become rather disjointed and if it went on for any length (which by your proposal, they would), almost unreadable.