As a presidential candidate in August 2015, Donald Trump huddled with a longtime friend, media executive David Pecker, in his cluttered 26th floor Trump Tower office and made a request.

What can you do to help my campaign? he asked, according to people familiar with the meeting.

Mr. Pecker, chief executive of American Media Inc., offered to use his National Enquirer tabloid to buy the silence of women if they tried to publicize alleged sexual encounters with Mr. Trump.

Less than a year later, Mr. Trump asked Mr. Pecker to quash the story of a former Playboy model who said they’d had an affair. Mr. Pecker’s company soon paid $150,000 to the model, Karen McDougal, to keep her from speaking publicly about it. Mr. Trump later thanked Mr. Pecker for the assistance.

The Trump Tower meeting and its aftermath are among several previously unreported instances in which Mr. Trump intervened directly to suppress stories about his alleged sexual encounters with women, according to interviews with three dozen people who have direct knowledge of the events or who have been briefed on them, as well as court papers, corporate records and other documents.

Taken together, the accounts refute a two-year pattern of denials by Mr. Trump, his legal team and his advisers that he was involved in payoffs to Ms. McDougal and a former adult-film star. They also raise the possibility that the president of the United States violated federal campaign-finance laws.

The Wall Street Journal found that Mr. Trump was involved in or briefed on nearly every step of the agreements. He directed deals in phone calls and meetings with his self-described fixer, Michael Cohen, and others. The U.S. attorney’s office in Manhattan has gathered evidence of Mr. Trump’s participation in the transactions.

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