Talk about a newspaperman’s sense of timing. President Trump has upended the Republican presidential calculus. He’s sidelined — at least for now — many of the intellectuals who had held sway in the party since the rise of Ronald Reagan. He’s launched an America First policy that rejects the instincts of the long-reigning neoconservatives. Even in victory the party is rethinking its core principles.

What a moment for George Melloan’s new book on the Wall Street Journal’s editorial page. “Free People, Free Markets,” just out from Encounter Books, is part history, part memoir — an insider’s account by one of America’s greatest editors. It sketches how the opinion pages of what became the nation’s largest — and most trusted — newspaper helped shape America. For conservatives seeking their bearings in the Age of Trump, it’s hard to imagine a better, more experienced guide than George Melloan.

The author was present at the creation of the editorial vision of the Journal’s most radical editor, Robert Bartley. Mr. Melloan, Bartley’s deputy, never kept an “office” per se. His desk was out in the open, the easier for editorial writers — and Bartley himself — to gather round him for the daily editorial meetings. It was Mr. Melloan who took notes and began to form the day’s lineup of editorials and op-ed pieces that influenced our national debate.

Mr. Melloan was there when the Journal started agitating for America to reject the Strategic Arms Limitation Treaty with the Soviet Union and to abandon the Cold War strategy known as Mutually Assured Destruction. In the wake of the collapse of the Bretton Woods system, Bartley and Mr. Melloan wrestled with the monetarist ideas of Milton Friedman and rejected floating exchange rates. Mr. Melloan was there for the Journal’s emergence as Israel’s greatest defender in the press. He was there for its famous campaign for supply-side economics.

The accession of supply-side economics was among the Journal’s most consequential scoops. It helped craft the policy mix of sound money and marginal tax cuts, which broke the stagflation that had set in under President Carter. At a lunch with Bartley, Mr. Melloan, and associate editor Tom Bray, the newly named Federal Reserve chairman, Paul Volcker, asked whether, in the battle against inflation, the Journal would stand with him when “there’s blood all over the floor”; it was Mr. Melloan who quickly answered for the paper: “Yes.”

Yet one of the best features of this book is the way Mr. Melloan teases from the Journal’s history certain editorial principles that have endured for generations. He opens his story in 1889, when the paper was formed in a basement on Broad Street in lower Manhattan. One of its first principles was the sanctity of contracts, of which we hear precious little today, even though it’s constitutional bedrock (marked in Article I, Section 10).

Charles Dow, who emerged as the early editorial voice of the partnership that also included Edward Jones and Charles Bergstresser, wrote of the contract obligation eloquently. Dow argued, as Melloan summarizes him, that “a slave couldn’t make a contract because he was not free to uphold its terms” and that “only a free man could enter into a contract,” making contracts, in their concept, among the “artifacts of freedom.”

That applies also to a second principle embraced by the Journal: sound money. In 1893, the paper helped repeal the Sherman Silver Purchase Act, an inflationary scheme. “Journal opinion editors today,” Mr. Melloan remarks, “would be overjoyed if they could achieve a monetary victory of that importance.” The Journal would feud for much of a century with the Federal Reserve and what Melloan calls its “artificial suppression of interest rates” that encourage “excessive borrowing, particularly by the government.”

The paper’s attachment to sound money pitted it against farmers and miners. Yet when, in 1902, the miners walked out of the coal pits of Pennsylvania, the Journal startled its readers by siding with the miners in the showdown over anthracite. Charles Dow, who had emerged as the voice of the paper, defended collective bargaining on the grounds that “a combination of labor is just as legal, just and moral as a combination of capital.”

Mr. Melloan also marks the Journal’s openness to such minimal levels of government regulation as seemed logical to protect market integrity and freedom. He quotes Thomas Woodlock, who succeeded Dow as the editorial voice and had done a stint as a member of the Interstate Commerce Commission, as reckoning that the paper “looked with favor” on the Interstate Commerce Act that, in 1887, gave the feds control over interstate rail rates.

Not that this book is blithe to the Journal’s errors, which, though few, have been notable. In 1928, it endorsed for president the engineer-turned-political-meddler Herbert Hoover, who helped precipitate the Great Depression by colluding with the Republicans in Congress in raising taxes and, as Mr. Melloan puts it in a wonderfully newspaperish solipsism, violating “the Journal’s free market principles” by signing the Smoot-Hawley tariff.

Nor does Mr. Melloan neglect to mention the Journal’s waffling on the eve of World War II. It worried that America could “muddle into war” (in respect of Munich, I’ve noted elsewhere, the Journal put its faith in the Kellogg-Briand Pact outlawing war). The paper’s otherwise visionary editor, Bernard Kilgore, Melloan notes, actually apologized for failing to read the public sentiment that, in 1940, elevated FDR to a third term.

Mr. Melloan’s handling of the Journal’s early history is knowing and savvy — one can almost see the newspaper’s institutional character being formed. In the decades since its blunder on Hoover, the paper has refrained from formally endorsing any presidential candidate. Instead it has stuck to endorsing ideas and principles, with remarkable fidelity over a long period of time.

That has enabled the paper to grant astounding discretion to its editorial page editors. I like to tell the story of Bretton Woods. During the 1944 monetary conference, the New York Times issued a brilliant series of editorials warning that Lord Keynes’s scheme was an inflation trap. Once Bretton Woods was ratified, though, the Times’ publisher, Arthur Hays Sulzberger, called in the editorial writer, Henry Hazlitt, and told him the paper would have to support it. Hazlitt quit.

It’s hard to imagine something like that happening to Bartley or Mr. Melloan. The Journal had been less prophetic than Hazlitt about the conference in New Hampshire. Once the deal was done, though, the Journal began a 70-year critique of the Bretton Woods institutions (particularly the IMF and the World Bank) — and often in a way that put the newspaper at odds with the Mandarins of the Republican Party and of Wall Street.

Another of my favorite examples of the Journal’s emerging character was glimpsed shortly after Eisenhower won the 1952 election. It was the last time a Republican candidate stood on a plank calling for gold convertibility of the dollar. Yet after winning on such a platform, Eisenhower waffled in the face of those who argued that repairing the dollar should wait until the post-war economy was stabilized.

Journal editors thought the way to stabilize the economy was precisely to repair the dollar. There is, as they put it, “ample reason to believe that the return of the United States to a gold-convertible currency would exert a more powerful influence on the side of stable world economy than anything else we could do.” Eisenhower’s failure to take the Journal’s advice was one of the things that precipitated the collapse of Bretton Woods.

It was just before that collapse that Mr. Melloan, in 1970, joined the editorial page. Then in 1972 the Journal’s brass reached over more senior figures to tap Bob Bartley, a relatively young editorial writer, as editor of the editorial page. So began the great Bartley-Melloan partnership, which changed the American debate on numerous fronts. Melloan spends more time on the tax and fiscal debate than the monetary issues, and for good reason.

The Journal’s role in fomenting the supply-side revolution has been widely recounted. What I like about Mr. Melloan’s telling of the story is its newspapermanliness. Bartley and Mr. Melloan championed the genre of the reported editorial. What is often derided as ideology was, in fact, a series of scoops that arose from an un-blinkered reporting of policy errors and an openness to new ideas and all kinds of life experience.

Bartley himself was the son of a teacher of veterinary medicine; Mr. Melloan was from a Midwestern family that had lost its farm in a cattle deal in 1927. Jude Wanniski, an irrepressible supply-side guru, was the son of a butcher and grandson of a coal miner who was a communist. Dan Henninger, now a columnist, had started at the New Republic and risen to chief editorial writer. Of Bartley and Mr. Melloan, Mr. Henninger remarked that the two taciturn Midwesterners communicated by osmosis.

In the case of Israel, Mr. Melloan’s contribution began well before he arrived at the editorial page and before Bartley had acceded to the editorship. Mr. Melloan had covered the 1967 Six Day War as a foreign correspondent. At the time, the Journal was critical of America for trying to “straddle,” to use Mr. Melloan’s word, the two sides; the paper faulted the United States for trying to prop up the Egyptian socialist Gamel Abel Nassar and, as Melloan put it, “getting only insults in return.”

Fourteen years later it was Mr. Melloan who drafted one of the Journal’s most famous editorials, supporting Israel’s 1981 decision to bomb Iraq’s nuclear reactor. The Journal had waited a day, until after the Times issued a diatribe condemning Israel for making a “sneak attack” and calling it an act of “inexcusable and short-sighted aggression.” The Times’ editor, Max Frankel, later acknowledged that the editorial was one of his paper’s “major mistakes.”

The Journal’s editorial, “Mourning the Bomb,” began by mocking the idea that “an atom bomb for Iraq” had “become the latest great cause célèbre of world opiniondom.” It went through the litany of Iraq’s crimes and sketched its dangerous intentions. “We all ought to get together,” the Journal said, “and send the Israelis a vote of thanks.” (Eventually, during the Gulf War, America’s sentiments of appreciation were expressed by Vice President Cheney.)

Yet for all the elan of the Bartley-Melloan-WSJ sallies on Israel, it would be inaccurate to suggest that the Journal was animated by Zionism per se. Bartley on a number of occasions described himself as acting out of a sense of realism and American interests. Mr. Melloan doesn’t address the point directly, but he confirms it en passant in the straightforward way in which he reprises his Middle East chapter.

In 1990, Mr. Melloan was sent to oversee the editorial pages’ foreign coverage from Brussels — or, as I like to quip, Bartley had finally had enough of the Soviet Union and sent Melloan over to deal with it. Quips aside, it’s hard to imagine a sweeter editorial writing assignment than Mr. Melloan’s last overseas tour. It capped a career that offers much to think about in the Time of Trump. Throughout it all Melloan emerged as one of journalism’s most articulate defenders of the free movement of trade, capital, and labor.

It is illuminating, particularly from the perspective of the Trump years, to be reminded by Mr. Melloan of how the Journal reacted to major crises, such as the Watergate scandal. It had fought Nixon on wage and price controls and other anti-market policies, but its early instinct was to defend Nixon, or at least the presidency, during the long battle mounted against him by the liberal papers. Once the evidence was in, though, the Journal dropped him suddenly and with no hand-wringing.

“The outcome of Watergate is a disastrous one for Richard Nixon, but it must be a heartening one for James Madison,” is the way the Journal put it in its editorial.

The Journal early on had adopted a skeptical view of the Vietnam escalations. That came to a head in 1968, when its chief editorial writer, Joe Evans, sat down at his typewriter and, without much ceremony, wrote an editorial that began: “We think the American people should be getting ready to accept, if they haven’t already, the prospect that the whole Vietnam effort may be doomed.” Bartley came to the view that the moral blunder was the assassination of Vietnam’s first president, Ngo Dinh Diem, and that the war was lost not on the battlefield but in the U.S. Congress.

Something for President Trump to mark. The Journal had been mockingly critical of Trump at the outset of his campaign and declined to endorse him. “The Wall Street Journal hasn’t endorsed a presidential candidate since 1928,” the paper reminded its readers, “and if we didn’t endorse Ronald Reagan we aren’t about to revive the practice for Mrs. Clinton or Mr. Trump.” Neither, though, did the paper throw in with the “resistance” against the decision of the voters.

Under editorial pager editor Paul Gigot, the Journal pursued instead a strategy foreshadowed in Mr. Melloan’s history. In the run-up to the campaign, the Times had announced that the old standard of traditional newspaper objectivity would not suffice. In contrast, the Journal stayed true to both its journalistic practices and its principles of free people and free markets. Mr. Melloan underlines all this in a gem of a book that adds up to a hopeful report at a time when so many are losing heart.

Mr. Lipsky, who spent 19 years on the Wall Street Journal, including eight years on its editorial board, is editor of The New York Sun. This review first appeared in the September/October 2017 number of the American Conservative.