I agree that the latest one, 4th to 5th, was "evolutionary", and a transition of similar magnitude or character (adjusted for the USA) is what I think we can anticipate. (Probably will involve more checks on the POTUS, though I hope not too many, and on party reign in the executive).
Arguably it could be our Third Republic, if you count the Civil War and Reconstruction as another transitionary phase where the nation transformed its cultural and institutions, as well as its Constitution.
However Trump leaves the presidency, I suppose the end of his administration will mark the proper (in hindsight) beginning to the event, and it will preoccupy most of the 2020s in its extent.
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