The now-defunct Trump University, the subject of one of Marco Rubio’s attacks on Donald J. Trump at the Republican presidential debate on Thursday night, was not a real university at all but a series of seminars held in hotels across the country that promised to share Mr. Trump’s real estate investing acumen with students. It is still embroiled in lawsuits accusing it of misrepresentation.

Those who ultimately bought premium packages paid as much as $35,000 for the privilege of additional training, called mentorships and apprenticeships.

“Seventy-six percent of the world’s millionaires made their fortunes in real estate,” Mr. Trump said in an email marketing blast sent to tens of thousands of potential customers. “Now it’s your turn. My father did it, I did it, and now I’m ready to teach you how to do it.”