Julian Zelizer is a history and public affairs professor at Princeton University, editor of "The Presidency of Barack Obama: A First Historical Assessment" and co-host of the "Politics & Polls" podcast. Follow him on Twitter: @julianzelizer. The opinions expressed in this commentary are those of the author. View more opinion articles on CNN.

(CNN) Bob Woodward's "Fear: Trump in the White House" is a runaway hit. The book has captured many of the Washington headlines since parts of it leaked out last week, and on Tuesday, its first day on sale, it sold more than 750,000 copies.

The Pulitzer Prize-winning reporter offers juicy nuggets about what life is like in the Oval Office. Even with a President who shocks the nation in real time throughout the 24-hour news cycle, Woodward managed to discover some jaw-droppers, such as Gary Cohn, former director of the White House National Economic Council, literally stealing a document from Trump's desk to protect the nation from what he viewed as potential danger.

But does Woodward's book really capture what is so remarkable about this presidency? In some ways, for all of its detail and anonymous sources, the book is utterly predictable. Like Michael Wolff's "Fire and Fury," Woodward's book, with much more precision, takes a deep dive into the parlor politics of Trump Land. But in doing so, he misses the big story.

Like so much of the news coverage that continually has its lens focused on political insiders, Woodward doesn't really address why it is that a highly unstable President, whose agenda revolves around white nationalism and "America First," can dominate US politics in 2018. Fifty years after the civil rights movement transformed the country by pushing it in a progressive direction on matters of social justice, we seem to have taken a massive step backward.

Why is this happening? The answers have less to do with the President than with everything that surrounds him. These are questions that demand the historian's interest in context rather than the reporter's thirst for detail. The questions need to start with the Republican Party, which has provided a safe home for the reactionary brand of politics that Donald Trump champions.

Read More