While reading this book, I mused quite a bit about history, and what it is that historians do. On this particular topic, you wouldn't think the facts are much in doubt. Progressivism's origins are relatively recent, not lost in the rubble of ancient societies. Everyone was paying plenty of attention at the time, and wrote down what they thought and observed. The facts wouldn't seem to have been much in doubt. And yet…
It turns out (and I should have realized) that historians are interpreters of history. They need to filter out important and pertinent from the trivial and irrelevant. And (since they are human) they are prone to the same failings as the rest of us: biases, hubris, laziness, …
I'm not a historian, not even close, and this book seems to be aimed at historians. But I trudged through it anyway. It's a very scholarly tome, one contribution to one side of a contentious (but slow-motion) debate, and (important disclaimer) I may have missed some things, and badly misinterpreted others.
Watson briefly discusses the origins of progressivism, making the interesting point that it incorporated two main new ideas. The first (typified by Woodrow Wilson in the late 19th century) was advocacy that American politics should break away from the stale old "Newtonian" framework described by the Declaration and the Constitution set up by the Founders, instead moving to a "Darwinian" approach of the "fittest" state surviving due to constant adaptation to dynamic social conditions. Darwinism being the new cool paradigm of the day.
Even though the "Darwinian" label was slapped on progressivism by Wilson and others, they seemed to ignore that actual evolution proceeded by sheer dumb luck; the progressive vision of preferred political/social development was very much an "intelligent design" deal, under the centralized command and control of wise bureaucrats guided by a president with powers unforeseen by the Founders.
The other thread was (somewhat surprisingly, given all the Darwinism) from many of the Protestant religious leaders of the day. Watson'a prime example here is Richard T. Ely, trained as an economist, but also the founder of the "Christian Social Union" which advocated "the application of Christian principles to the social problems of the world." Very much into "immanentizing the eschaton", if you know what I mean.
But (bottom line) these disparate visions both advocated diligent state-directed social engineering, full of the hubris that implies. "We know what the future should look like, so toss us the keys, we're driving."
Despite the subtitle, book proceeds to not discuss very much the actual history of progressivism from its intellectual origins. (For example, Robert M. La Follette does not even rate an index entry.) Instead, Watson proceeds to review what other historians said about the Progressive Era. His main point here seems to be that those historians swept the underlying anti-Founder tenets of progressivism under the rug. (To a large extent, they agreed with that.) And there's little discussion of the general illiberalism of the early Progressives. You'll have to read Thomas C. Leonard's Illiberal Reformers for that sordid story.
Watson finishes up with a look at the "revisionist" Claremont/McKenna scholars who corrected this tilted view somewhat. (I think Watson himself is in this group.)
Again, Goodreads encourages me to rate the book subjectively, and except for the early stuff I found it (overall) less than interesting.