As I understand it the various EU treaties are not intended to create a United States of Europe. But perhaps some learnings could be found by looking at what it took to get the U.S. constitution ratified.

For one thing, there was an identified "other" (Britain) that had just recently been fought in an expensive and exhausting war. Europe doesn't currently have such a generally understood competitor, so perhaps the urgency of "doing something" is not so urgent.

Even with that in place, in America there was a lot of opposition to collecting the colonies into a single country. A lot of manipulation was required to get the constitution ratified, and it wasn't put to a popular vote. Even then, it was a close call in most states.

Also, the U.S. constitution is a general statement of principles, with a clear intellectual base. It sets up a system founded on certain axioms, but leaves the vast majority of the details to be worked out later. The E.U. treaties are treaties, not statements of principle.

Perhaps the recent failures of the treaty votes will trigger a reconsideration of whether the current E.U. setup is really viable. Do they re-open the question of whether there SHOULD be a U.S.E.?