Less than four hours before President Donald Trump’s announcement that he was pausing tariffs sent markets soaring, he posted online telling his 9.4 million followers that it was a good time to buy.

“THIS IS A GREAT TIME TO BUY!!! DJT” he posted on his social media site, Truth Social, at 9.37am Eastern time on Wednesday. Shortly after 1pm, he announced on the same site that he would pause most new tariffs, causing the ailing stock markets to sharply rise.

Democrats are now accusing Trump of “market manipulation,” and the term is trending on the social media platform X, with more than 33,000 posts.

“The President of the United States is literally engaging in the world’s biggest market manipulation scheme,” the Democrats from the House Committee on Financial Services posted on X on Wednesday afternoon.

Trump has long drawn questions from ethics experts about his various business holdings, and after he was elected he made no promises to divest from any of his financial interests. Trump’s assets are in a trust managed by his children, the White House said.

The president holds much of his net worth in his stake in Truth Social’s parent company, Trump Media & Technology Group. That company trades at the ticker DJT, the president’s initials and the sign-off he used in Wednesday morning’s Truth Social post.

The company’s stock rallied with the broader markets after the tariff announcement, closing the day up more than 21%.

The White House pushed back on Wednesday on the idea that Trump improperly manipulated the markets.

“It is the responsibility of the President of the United States to reassure the markets and Americans about their economic security in the face of non-stop media fear mongering,” White House spokesman Kush Desai said in an emailed statement.

It’s not the first time Trump has encouraged people to buy stock - amid a market slide in 2018, during his first term, he told reporters it was a “tremendous opportunity to buy.”

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In an interview, Representative Steven Horsford (Democrat, Nevada) said Trump’s post raised suspicion that members of the administration may be trading on information about tariffs in advance of it being disclosed to the public.

“It’s my concern that the administration may be using trade policy to give insider information to individuals before impending actions or inactions,” he said. “If it occurred, that is market manipulation.”

Horsford said he is calling for a full investigation into who may have profited from this information, but he acknowledged that carrying out such a probe would be difficult when the administration has fired many of the inspectors general who normally provide such oversight.

Typically, cases of potential market manipulation are first investigated by exchanges, including Nasdaq and the New York Stock Exchange, whose investigators look for trading anomalies and unusual patterns by individual traders, said James Angel, a finance professor at Georgetown University. If they find evidence of unusual activity they report it to the Securities and Exchange Commission, which determines whether enough evidence exists to build a case against someone for improper disclosures or trades, he said.

In this case, it’s unclear whom the SEC would build a case against because nobody knows who may have benefited from Trump’s post. Officers and large shareholders of companies are required to disclose their trades, but private individuals who may have benefited from Trump’s post are generally not required to disclose that information to the public.

As the key decision-maker around tariff policy, Trump did have access to information that regulators would consider “material” to the value of stocks when he made his “great time to buy” post. However, his comment was so general that it would be difficult for anyone to build a case that it represented a disclosure violation, Angel said.

“Our securities laws outlaw any kind of fraud or manipulation, but it’s often hard to prove manipulation,” Angel said. “I doubt regulators would go after someone who says it’s a good time to buy.”

But others say the President is opening himself up to scrutiny with his post.

Richard Painter, a former chief ethics lawyer for the George W. Bush White House, said Trump was taking big risks by posting on social media in ways that explicitly referred to the markets. Trump exposes himself to allegations that he’s engaging in market manipulation, potentially giving insider tips “or other forms of securities fraud,” he said.

The post could also trigger federal investigations or private lawsuits from any investors who lose money on his recommendation.

“He’s playing with fire,” Painter said, adding that he didn’t believe the conduct would count as “official acts” as part of his duties as president.

Major stock indexes climbed sharply after days of losses following the tariff announcements last week. The S&P 500 closed up 9.5%, and the narrower Dow Jones Industrial Average rose nearly 8%.

Trump’s posts may have at least one less visible effect than the stock market swings.

“After today, a bunch of hedge funds are going to have their computers following Truth Social and trading on the President’s tweets,” Angel said.