The tantalizing text message was sent by a lawyer for a former Playboy model to the editor of The National Enquirer.

“I have blockbuster Trump story,” read the message sent in 2016 by the Los Angeles lawyer, Keith Davidson, who was on the witness stand as prosecutors posted it Tuesday morning for jurors at Donald J. Trump’s criminal trial.

The editor, Dylan Howard, asked in response: “did he cheat.”

The texts were an evocative beginning to testimony that laid bare the seamy ways celebrity scandal is leveraged and sold. In this case, it was a deal negotiated by Mr. Davidson for Karen McDougal, the model, who wanted to rejuvenate her career by leveraging her story of a romantic affair with Mr. Trump. She has said the liaison began in 2006 after he was already married to his current wife, Melania.

The Enquirer’s parent company paid her $150,000 for the rights to that story, but never published it, using a tactic called “catch-and-kill.” The Enquirer’s publisher has previously testified that he used the method to suppress negative news about Mr. Trump during the 2016 election.

Tuesday afternoon, Mr. Davidson began to testify about his representation of Stormy Daniels, a porn star whose hush-money deal is at the center of the case. Ms. Daniels was paid $130,000 by Michael Cohen, Mr. Trump’s longtime lawyer and fixer, to remain silent about her account of sex with Mr. Trump, also in 2006.

The payments for both women were initially wired to Mr. Davidson, who no longer represents either.

The Daniels deal is at the center of this criminal trial, in which Mr. Trump is accused of falsifying business records to cover up his repayment of the hush money to Mr. Cohen. He has denied wrongdoing, and said he did not have sex with Ms. Daniels or an affair with Ms. McDougal.