In the face of the forces rending the United States, Lepore depicts it as a unitary society with a distinct and laudable set of civic ideals, one whose past can be intelligibly told as a single story.  

Can Jill Lepore do what historians used to do in their spare time, namely, write a single-volume history of the United States that is both honest and uplifting? Lepore, as this reviewer puts it, faces a triple challenge: she

finds herself in the awkward position of espousing patriotism at a moment of cruel nationalism, of explaining why radicalism doesn’t work at just the time radicals on all sides are gaining clout, and of insisting that the nation is the most relevant geographical unit while storms, droughts, and heat waves make a mockery of political borders. 

And so she tries to write a kind of historiographical epic. In doing so she dallies with the dangerous, unguarded "we," as in "we believe" or "we hold these truths," etc..  Now, academics are not so much trained as conditioned, like attack dogs, to hunt out the faintest scent of "we" claims, and to "expose" them as presuming a unity that may not be warranted.  Well, I totally get the danger of doing so.  But rhetorically speaking, "we" is a helluva drug for academics, or really anyone trying to speak to a public audience.  (And Bernard Williams decades ago suggested, wisely, that the "we" can be understood invitationally and aspirationally, not presumptuously.)  I'm willing to give her the benefit of the doubt there.

Her frank use of the national frame allows her to speak to people who aren't so totally hep to globalization, big data, or the anthropocene, in which un-hep category is about 97 % of the human race, and also about that many Americans:

While her colleagues are embarking on their free-form jazz odysseys, decentering the nation by writing books about oceans, most readers still see the world in terms of nations, and they want history written accordingly. “They can get it from scholars or they can get it from demagogues, but get it they will,” Lepore warns.

So as a piece of public scholarship--an intervention not only into historiographical debates about American history but a contribution to public self-understanding in America--Lepore is trying to do something unusual.  Furthermore, 

Driving the demagogues out of the Barnes & Noble will require more than just taking back the nation as an object of serious historical inquiry. Lepore also sees a need to show that object in a more flattering light. Whereas many of her colleagues narrate US history as a tragedy and a chronicle of oppression, Lepore sets out to capture a fuller range of feeling.

The picture she offers, the review says, a national history that does not flinch from evil, but tries as well (not instead, mind you) to highlight moments of hope and progress.

This picture leads her towards a critique of younger radicals out there these days.  She presents them as politically reckless and emotionally feckless, unable to discriminate important from superficial, prone to being "triggered," and eager to scold and "call out" those who do not sufficiently manifest their righteousness for public consunption.  (I don't know if that's fair to Lepore, but I could totally see someone of her age and academic training, which is not unakin to my own, holding views of that sort.)  The reviewer suggests Lepore hasn't really taken her opponents seriously, hasn't really heard their vision: 

radicals tend to have a different understanding. In their view, the United States—a settler empire carved out of Native lands by rich white men, many of whom enslaved others—was not particularly egalitarian in its origins. If it’s a better society today, this is because activists made seemingly unrealistic demands and fought for them. Stark conflict has been essential to progress, and the times of greatest national division—the 1860s, the 1960s and ’70s—have also been times of major progressive victories like the abolition of slavery and the establishment of reproductive rights. For a radical, this is not the time to mend rifts or make compromises. It’s a time of crisis—and when it comes to the threat of global warming, an existential one. It’s also a rare chance to achieve root-and-branch change with regard to the environment, the economy, gender, sexuality, and race. If what is needed is an overhaul rather than an adjustment, then the ideals and methods of 18th century men—“these truths”—may not be the best guides.

What's interesting here--to put in an oar on Lepore's side, so to speak (so long as that doesn't make us go in circles,  metaphorically or otherwise), is that the descriptive judgments in that paragraph are pretty de-contextualized.  Certainly the US was not in the 18th century "particularly egalitarian," compared to us today.  But compared to, where?  The United Kingdom of George the Third?  Tokugawa Japan?  the Ottoman Empire?  Thinking of that question leads, I think, to a different answer.  Liberal politics is about compromise, and Lepore imagines that a renovated liberal history is what is needed today.  In that I suspect she is a "rebel," in Camus's sense of the term, not a "revolutionary": one who seeks partial victories and accommodations to deplorables, in part out of fear of asking so much as to destroy much more than can be achieved. 

The contemporary historiographical scene doesn't seem especially amenable to that kind of historiography.  It will be interesting to follow the reception of Lepore's book.