It’s a question that has perplexed historians for centuries: why did Madison, whose zeal for federalism in some respects initially exceeded Hamilton’s, change sides? I posted on this issue back in 2016, but with the advantage of nine years of additional reading, I’m going to try it again.
I think there are two reasons. First, Madison’s intense federal phase coincided with Jefferson’s tenure in Paris. Hamilton later accused Madison of being, I believe, “the handmaiden to a greater mistress;” there may have been some truth to this. But the more important reason was that Madison’s focus was less on strengthening the central authority and more on the protection of individual rights, the greatest threat to which in 1787 came from the states. When the new federal government started implementing an agenda that went well beyond checking state excesses, it was logical for Madison to flip against it.