FILE - In this Oct. 15, 2019, file photo, Donald Trump, Jr. speaks to supporters of his father, President Donald Trump, during a panel discussion in San Antonio. President Donald Trump has accused former Vice President Joe Biden of major ethical lapses and railed against Biden’s son for allegedly profiting off his father’s office. But on Nov. 4, Trump used his Twitter feed to publicize a new book by his eldest son, Donald Trump Jr., telling his 66.5 million followers that they should “Go order it today!” (AP Photo/Eric Gay, File)

WASHINGTON — President Donald Trump has accused former Vice President Joe Biden of major ethical lapses and railed against Biden’s son for allegedly profiting off his father’s office.

But on Monday, Trump used his Twitter feed to publicize a new book by his eldest son, Donald Trump Jr., telling his 66.5 million followers that they should “Go order it today!”

“My son, @DonaldJTrumpJr is coming out with a new book, “Triggered: How the Left Thrives on Hate and Wants to Silence Us” – available tomorrow, November 5th!” Trump wrote on Monday, calling it a “great new book that I highly recommend for ALL to read.”

That kind of promotional tweet would be a violation of ethics rules if it had come from any federal employee other than the president, said Liz Hempowicz, the director of public policy at the Project on Government Oversight, a nonpartisan government watchdog group.

“Frankly he’s using his Twitter account to try to financially benefit his son,” she said Monday. “That’s not only distasteful, but it’s a misuse of public office and it would be an official misuse of public office if it was anyone other than the president.”

The tweet also highlights a well-practiced tactic of Trump trying to turn a weakness into an attack on his opponents.

In this case, Trump has zeroed in on Biden’s son Hunter, going as far as to ask foreign governments, including Ukraine and China, to investigate the Biden family’s business dealings. Those efforts helped spark the impeachment inquiry into his conduct.

Biden is a leading contender for the Democratic nomination and could face Trump in the general election next year.

“The Biden family was PAID OFF, pure and simple!” Trump insisted in a tweet last month, despite no evidence suggesting that the former vice president received any payments or that Hunter Biden did anything illegal. The younger Biden has acknowledged he displayed poor judgment when he took a post on the board of a Ukrainian energy firm, Burisma, after his father became the Obama administration’s point person on U.S.-Ukraine relations.