Among the many titles in the white supremacist canon, “The Turner Diaries” is the most important and one of the few titles recognized by mainstream Americans. Written by William Pierce, then-head of the neo-Nazi group the National Alliance, and published in 1978 under the pseudonym Andrew Macdonald, it is a fictitious diary written by its hero, Earl Turner. A young white man, Turner joins a terrorist group called “the Order,” which commits a series of attacks designed to incite a wider race war. One thing leads to another and a nuclear-armed battle is waged between Turner’s forces and the government, which in Mr. Pierce’s telling is run by Jews and blacks. The plot climaxes with the establishment of a white ethno-state, and Turner is martyred. The novel ends with a memorial: “He gained immortality for himself on that dark November day,” it reads,

and in so doing he helped greatly to assure that his race would survive and prosper, that the Organization would achieve its worldwide political and military goals, and that the Order would spread its wise and benevolent rule over the earth for all time to come.

“The Turner Diaries” was an innovation of sorts, a hybrid of fantasy and how-to, and it has inspired hundreds of terrorist attacks in the United States and Europe, including the 1995 Oklahoma City bombing, which killed 168 people and injured 684 others. The attack was a copycat of the one Mr. Pierce outlined in the book, right down to the time of day and type of explosives used. Pages of the book were found in a plastic bag in the car of the plot’s leader, Timothy McVeigh. The mainstream attention caused a kind of miniboom in the genre that lasted into the early 2000s, as other would-be authors, Mr. Kendall and Ms. Williams among them, tried their hand at writing fiction.

Sitting beside “The Turner Diaries” at the top of the white supremacist best-seller list is Jean Raspail’s 1973 novel, “The Camp of the Saints.” It is a brooding parable that warns of the dangers of immigration and is something of a standout for being relatively well written, even in translation from the original French. Mr. Raspail’s caustic, often-humorous, ellipses-littered prose is reminiscent of that of his fellow countryman Louis-Ferdinand Céline, whose own history as a Nazi sympathizer cast a shadow over his otherwise brilliant work.

The book’s central “problem” begins in Belgium, where priests are encouraging the adoption of Indian children as a form of charity. In an early scene, a roiling sea of desperate Indian mothers — “wretched creatures” — storms the gates of the Belgian embassy in Kolkata, each with a child in her outstretched arms. The country is soon swamped with these adoptions, and authorities announce an end to the policy.

But it’s too late; the mob gains strength as the Indians are joined by Arabs and other nonwhites. They eventually grow to one million strong, board a flotilla and set sail for France. The country’s liberal government hesitates to defend against the onslaught, and as it stammers and acquiesces, the immigrants begin to enter the country. France’s whites retreat northward, but are eventually absorbed by the demographic shift, and the trend spreads throughout Europe, as indigenous populations and other “hoards” are inspired to rise up. They eventually take over the world, erasing the white race from existence.

White supremacists seem convinced that the novels’ “white genocide” is coming to life, and are petitioning Mr. Trump for help. This past spring, Andrew Anglin, the deeply sinister and darkly clever force behind Daily Stormer, the most Millennial-y neo-Nazi site on the web, started to spread the news of a “migrant caravan” that was moving through Central America, toward the United States-Mexico border. It was a protest march, organized by the Central American pro-immigration activist group Pueblo Sin Fronteras. The march has taken place every year since 2010 without ever getting much traction in the press.

But Mr. Anglin saw an opportunity in the implication of a literal enactment of “The Camp of the Saints.” He rallied his troll army to petition Mr. Trump to use the word “caravans” publicly, and on April 1, he did. In fact, he and Vice President Mike Pence used the word multiple times, then issued an order to send the National Guard to the border. The story dominated the news cycle for days, and Mr. Anglin took a well-deserved victory lap, bragging that “the media was not talking about this, only the alt-right was, and Trump is posting about it — so he does hear us.”