Composed, unwavering, yet sometimes tearful, Ms. McDougal told a detailed story about a relationship that was based on love — “he always told me he loved me,” she said — and was facilitated by one of Mr. Trump’s bodyguards.

She described herself as a Republican and said she voted for Mr. Trump in November, describing him as “brilliant” and “charming” and someone she loved enough to even consider marrying. She said she was now eager to tell her story because it was already known and she wanted the chance to tell it herself.

Ms. McDougal said she first met Mr. Trump when he filmed an episode of “Celebrity Apprentice” at the Playboy Mansion in 2006, where they struck up conversation and he asked for her number.

She said they had theirgolf course home in New Jersey. I went to his home in New York.” At one party, she met his son Eric, and posed with him in a picture, she said. At another, at the Playboy Mansion, she posed for a picture with Mr. Trump, Melania Trump, Mr. Trump’s daughter Ivanka and other people, keeping her distance from Mrs. Trump as best she could, she said.

Ms. McDougal said Mr. Trump had compared her, favorably, to his daughter. “He said I was beautiful like her and, ‘You’re a smart girl,’” she said.