On Wednesday, responding to Mr. Spicer’s comments, Nordstrom maintained that it had pulled Ms. Trump’s products based on their declining sales performance. The company said it informed Ms. Trump of its decision in early January.

“Over the past year, and particularly in the last half of 2016, sales of the brand have steadily declined to the point where it didn’t make good business sense for us to continue with the line for now,” the Nordstrom statement said. “We’ve had a great relationship with the Ivanka Trump team.”

As Mr. Trump has noted several times, the president is exempt from conflict of interest provisions in federal law that prohibit other government officials from using their positions to benefit themselves or their family members financially. So even if his post was meant to intimidate Nordstrom or other retailers that still work with Ivanka Trump, it probably does not violate conflict of interest rules, said ethics experts, who nonetheless called it inappropriate.

“It is a total misuse of presidential power,” said Lawrence M. Noble, the general counsel of the Campaign Legal Center and formerly the top lawyer at the Federal Election Commission. “He is really bringing to bear the whole weight of the office of president on a business decision. Take another company that is considering whether or not to drop her line — they obviously are going to ask themselves if they want to be attacked by the president.”

Mr. Trump’s blast at Nordstrom came two days after his wife, Melania, filed a libel lawsuit that described her “multiyear term” as “one of the most photographed women in the world” — an apparent reference to her status as a candidate’s wife and now first lady — as a lucrative business opportunity. And Mr. Spicer, the White House spokesman, has urged people to visit the Trump International Hotel in Washington, which opened late last year.

Robert Weissman, president of Public Citizen, a group that promotes ethics in government, said Mr. Trump’s swipe at Nordstrom was not a major issue in itself. But Mr. Weissman said it demonstrates that as president, Mr. Trump continues to have multiple conflicts of interest with his own and his family’s business interests. Mr. Trump refuses to sell his assets or put them into a blind trust, but he has said that he has ceded operation of his businesses to his adult sons, Donald Jr. and Eric.

“He has committed to severing himself from the family business operations,” Mr. Weissman said. “That is obviously not the case.”