I'm gonna go with the old saying, always follow the money. A one day event would pound that reality into the system in no uncertain terms. The candidate with the most money upfront, before even one vote is cast will be the nominee. Yes, I realize that's already a big part of the whole process as it's in place currently, but a single day vote will make it even worse.
Hillary has alreay been working for a long time to get her war chest ready. If you can think of the name of any other Democrat in a similar position, put their name on the table.
Also, if the National Primary did not result in an absolute majority for any candidate, then all the leading candidates would have until their Conventions (up to 60 days) to sort out the best candidate to pick. Consider that John Kerry has more money (when you throw in his wife's assets) than any other candidate in US history. Yet he is about to lose.
That proves both of my main points.
John / Billybob