(Reuters) -Shares of Republican candidate Donald Trump's company that owns the Truth Social slumped 15% in premarket trading on Wednesday as betting odds of a win for Democratic candidate Kamala Harris grew after a combative presidential debate.

Harris put Trump on the defensive with a stream of attacks on his fitness for office, his support of abortion restrictions and his myriad legal woes, prompting a visibly angry Trump to deliver a series of falsehood-filled retorts.

Trump has a more than 50% stake in Trump Media & Technology Group, which has a market value of $3.7 billion. Its shares are popular among retail traders and sensitive to the former president's chances of a win in the 2024 election.

The stock has slumped nearly 60% since mid-July as Harris' chances improved against Trump after she replaced President Joe Biden as the Democratic candidate.

After the debate, pricing for a Trump victory slipped by 6 cents to 47 cents with a potential $1 payout on online betting site PredictIt, while Harris' odds rose to 57 cents from 53 cents.

"At this point, DJT is the betting stock for Trump winning," said Matthew Tuttle, CEO of Tuttle Capital Management.

Harris' candidacy also received a boost after pop megastar Taylor Swift told her 280 million Instagram followers in a post that she will vote for the Democratic candidate.

"The U.S. Presidential debate achieved its goal by providing a decisive edge to one of the candidates in what has been an exceptionally close race," said Charu Chanana, global market strategist at investment platform Saxo.

Trump Media's valuation equals more than 900 times the money-losing company's revenue of $4.1 million in 2023, far exceeding the worth of companies with bigger revenue.

For instance, Meta Platforms, which generated $131.9 billion from goods and services in 2023, has a price-to-revenue valuation of 9.6, according to LSEG data.

UPCOMING LOCK-UP EXPIRY

Since its listing through a reverse merger with a blank check firm in March, TMTG's market value has jumped as much as $9.2 billion as expectations of Trump victory rose. The stock has slumped 76% from its March peak.

An upcoming shareholder lock-up expiry could allow Trump and other investors to offload some shares as early as next week, potentially increasing the supply of shares and adding more pressure on the stock.

If the stock price remains at or above $12 for any 20 trading days from Aug. 22, then Trump will be free to sell shares beginning Sept. 20. Otherwise, the six-month lock-up expires on Sept. 25. The stock was last trading at $15.73.

"If he wins (the election) he doesn't have to sell his shares and DJT can grow into something. If he loses, he has to sell his shares to pay legal bills and it is unlikely DJT is a going concern," Tuttle said.