During the Progressive era, many politicians began to feel the need for a national primary system. Such a system would involve holding all presidential primaries on the same day - as opposed to the current system where the primaries and caucuses are held over a period of many months. In 1915, President Wilson supported this reform in the form of a bill. Ohio Senator Atlee Pomerene disagreed, arguing in favor of a constitutional amendment instead. Neither man's idea won out and ultimately the proposal went nowhere. But what if the US had implemented a national primary system during this period? What impact would this have on presidential elections from 1916 until today?
 
Initially it might just be a different kind of uneven than the current system. It seems likely the “favorite son” model would propagate readily in this period, leading to perhaps as many as a couple dozen men with direct control over big chunks of votes and maybe just one or two candidates trying to compete nationally. They’d sit down and broker a back room deal at the convention.

You could start to see bloc alliances form, such as one in New England, one in at least the Deep South if not the whole Confederacy, maybe a western bloc. It might highlight the need for an end to the fptp method earlier, say by the 1950s or so. Or it might serve as a cover to back room dealings as an expression of states rights and keep the plebs out of the drivers seat for even longer than OTL.
 
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