The author of the book "Clinton Cash" on Thursday criticized President Trump and his team's comments about Ivanka Trump's line of clothing and accessories.

“They’ve crossed a very, very important bright line, and it’s not good," Peter Schweizer told The Washington Post.

"To encourage Americans to buy goods from companies owned by the first family is totally out of bounds and needs to stop," added Schweizer, whose book was critical of donations to the Clinton Foundation.

He said the Trumps clearly feel "some of this is related to politics."

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"But whether that’s true or not, these marketing battles need to be fought by Ivanka and her company," he said.

"They cannot and should not be fought by government employees and the White House ... It’s time to move beyond the mindset and the role of a businessman and assume the mantle of commander of chief.”

His comments come after the president's top aide, Kellyanne Conway, on Thursday promoted Ivanka Trump's line of clothing and accessories during an interview on "Fox & Friends."

"Go buy Ivanka's stuff, is what I would tell you," Conway said. "I hate shopping, but I'm going to go get some for myself today."

"I'm going to give it a free commercial here, go buy it today," she said.

President Trump on Wednesday lashed out at Nordstrom for dropping his daughter's clothing line.