When Donald Trump Jr.’s new book “Triggered” appeared at the top of the New York Times best-seller list this month, a debate erupted over how and why it had claimed the No. 1 spot.

The book, a broad attack on his critics, Democrats and the news media, was published on Nov. 5. The following week, it topped the list. But some skeptics noted that Mr. Trump had gotten a boost from his father’s Twitter feed and from the Republican National Committee, which emailed supporters the day the book came out, asking them to purchase signed copies and touting it as the book the “left doesn’t want you to read.”

Others noted a tiny dagger symbol that appeared next to the title on the list, indicating that bulk purchases of the book had boosted its ranking. (Of the 10 nonfiction hardcover titles currently on The Times’s best-seller list, “Triggered” is the only one featuring that symbol.) Some of Mr. Trump’s supporters pushed back on social media and anonymously to Fox News, saying that even without bulk sales, “Triggered” would still top the list.

“We haven’t made a large bulk purchase, but are ordering copies to keep up with demand,” Mike Reed, an R.N.C. spokesman, said two days after the fund-raising email promoting “Triggered” was sent. “Each book is sold to an individual who supports the Republican Party.”