Trump's attack on Nordstrom blurs the line between the Oval Office and the family business

With his Twitter blast at Nordstrom, President Donald Trump sparked fresh concerns that he and his family are using the Oval Office for personal gain.

Trump accused the department store chain on Wednesday of treating his daughter Ivanka "unfairly," prompting its stock to drop briefly before it recovered. The president's tweet came days after Nordstrom said it would not sell his daughter's brand in the upcoming season due to sagging performance.

Trump: My daughter Ivanka has been treated so unfairly by @Nordstrom. She is a great person -- always pushing me to do the right thing! Terrible!

Trump's tweet, later distributed by the official "@POTUS" account, pulled him back into a debate over whether he did enough to distance himself from his family's businesses when he took office. The president chose not to divest from the Trump Organization, handing control to his two eldest sons and a company executive.

While the Trump Organization said Ivanka Trump stepped down from her roles there, she licenses her name to merchandise manufacturers, who then sell products at stores like Nordstrom and Macy's, according to The New York Times. It's not clear if she still receives royalties from her clothing licensing.

Trump's criticism of a company that distanced itself from his daughter's brand shows "un-presidential behavior and potentially much worse," said Richard Painter, a former top White House ethics lawyer under President George W. Bush.

"It is the use of public office for private gain," he said.

Later Wednesday, White House spokesman Sean Spicer called Nordstrom's move an "attack" on Ivanka Trump based on her father's policies and argued that he should have the ability to defend her. Asked whether Nordstrom's decision matters since Ivanka Trump said she stepped down from her companies, Spicer said it still damages a brand that carries her name.

"I think this was less about the family business than an attack on his daughter," the White House press secretary said.

In a statement Wednesday, Nordstrom said it made the decision because "sales of the brand have steadily declined," adding that "Ivanka was personally informed of our decision in early January." Nordstrom and other companies faced pressure as part of an effort by some consumers to avoid businesses with connections to the Trump family.

Ivanka Trump's brand makes the largest share of its sales from licensed clothing like the products sold at department stores, according to the Times. Her father also increasingly turned to brand licensing in his ventures before he took office.

Painter added that Trump's comments prompt concerns about the potential for insider trading if anyone knew to short the stock before Trump's tweet. Still, there is no indication that any improper trading took place around the time of the tweet.

Sen. Bob Casey, D-Pa., also raised ethics concerns after Trump's attack, tagging the independent Office of Government Ethics in response to the president's tweet. The agency has heavily criticized Trump for not divesting from his businesses or establishing a blind trust when he took office.

Casey: CC: @ OfficeGovEthics

House Democratic leader Nancy Pelosi, D-Calif., also called Trump's comments "inappropriate."

Since his electoral win in November, Trump has rightfully noted that the president is exempt from criminal conflict of interest laws.

Ivanka Trump's brand did not immediately respond to requests for comment. The OGE declined to comment.

Trump's Nordstrom attack marks the second time in recent days that the first family has prompted ethics concerns. In filings that are part of a libel lawsuit that first lady Melania Trump filed against the Daily Mail tabloid, her lawyers argue that her position could help her grow her personal brand, according to The Associated Press.

While her attorney said she had no intention of profiting from her standing, she has not stepped down from her brand, the AP said. For example, she was still listed on New York filings for companies that managed $15,000 to $50,000 in royalties from her accessories line, according to financial disclosures filed in May.

Separately on Wednesday, The New York Times reported that TJX Companies, the parent of T.J. Maxx and Marshalls, instructed employees to throw away Ivanka Trump signs and stop displaying Ivanka Trump merchandise separately.

WATCH: Analyst weighs in on Nordstrom-Trump conflict: It's not personal, it's product