In this May 16, 2019, photo, President Donald Trump speaks in the Rose Garden of the White House in Washington. For all Trump’s talk of winning, his lawyers are using a legal argument that many scholars say is a pretty sure loser to try to defy congressional attempts to investigate him. Credit: Manuel Balce Ceneta | AP

President Donald Trump has taken a unique approach to promoting literacy across America. Every so often, he tweets about a new book hitting the shelves, sometimes encouraging his more than 60 million followers to go buy a copy.

The presidentially-approved literature is usually authored by supportive voices in politics or the media, or focused on Trump’s ascendance to and service in the highest office of the land. The promoted works include “ Liars, Leakers and Liberals: the Case Against the Anti-Trump Conspiracy” by Fox News host Jeanine Pirro and “ The Briefing: Politics, the Press and the President” by former Trump Press Secretary Sean Spicer.

Most recently, Trump endorsed “Sacred Duty,” a book by Republican Sen. Tom Cotton about the Army unit that honors fallen servicemembers at Arlington National Cemetery. While Cotton’s book very well may be worth a read, the president’s promotional tone, trumpeting not just the book’s substance but also its sales, has us scratching our heads.

“Our great Senator (and Star) from the State of Arkansas, @TomCottonAR, has just completed a wonderful book, ‘Sacred Duty,’ about Arlington National Cemetery and the men and women who serve with such love and devotion,” Trump tweeted on May 14. “On sale today, make it big!”

It’s not unprecedented, or unwelcome, for presidents to release a list of suggested reading material. But this type of endorsement, with an unabashed emphasis on boosting sales of a specific product, raises some ethical questions.

For pretty much any other federal employee, using a public office to endorse a product for private gain is prohibited. Presidents, however, are exempt from those ethics laws. So Trump is fine here, legally speaking. But operating within the law should be the lowest standard we set for this or any American president. We should expect and demand that our leaders act ethically, not just legally.

You don’t have to read between the lines to see that the president isn’t simply endorsing the message of Cotton’s book, he’s actively working to increase profits for a supportive member of Congress. That’s not a good look for American democracy, even though it’s totally legal in this case.

We’re not looking for an investigation, or even for Trump to stop his book recommendations. In fact, it’s great that he is giving us a window into books he finds valuable, and promoting reading in the process. But it’s not too much to ask that our commander-in-chief treat his platform as a solemn responsibility rather than an opportunity to boost book sales for people he likes.

Incessant calls for impeachment and further investigation of the administration, often based in dislike of the president rather than facts or the pursuit thereof, have caused outrage fatigue for many people around the country — both those who are outraged, and those who are tired of hearing about the outrage. So it’s easy to let a relatively small issue like these book-related tweets slide by largely unnoticed.

But this type of product endorsement by a sitting president isn’t normal, and it shouldn’t be treated as such. It’s not a constitutional crisis or a national emergency, but it reeks of the very swamp tactics of quid-pro-quo that Trump campaigned against in 2016. And it’s a symptom of a much larger slide away from ethical norms in a political environment where the bar wasn’t particularly high to begin with.