Donald Trump is undeniably a skilled salesman—his powers of persuasion are a big part of how he got to the White House. Yet despite being a bestselling author himself, the president is not much of a bookseller. Friday morning, the writer Nick Adams received what you might expect to be pretty much the greatest endorsement ever: On Twitter, Donald Trump called his book Green Card Warrior a must-read.

Yet a little after 10 am eastern time, some three hours after Trump tweeted his critical praise, Adams’ book remains mired at almost #19,000 on the Amazon sales list.