HOUSTON — They still talk about the Saturday night here 27 years ago when Donald J. Trump partied with former President Richard M. Nixon.

Dressed in tuxedos, they sang “Happy Birthday” to Texas royalty — former Gov. John B. Connally and his wife, Nellie, whose birthdays were a few days apart — as Nixon played the tune on a white baby grand piano. They dined at Tony’s, the “21” Club of Houston, and Nixon was so fond of the cannelloni pasta that he asked the owner, Tony Vallone, to write the recipe for him on a yellow legal pad. And when it was all over, Mr. Trump flew Nixon back to New York on his 727 private jet.

It happened one weekend in March 1989.

It was one of Nixon’s first public appearances since the Watergate scandal had forced him to resign in 1974. And it was one of Mr. Trump’s first presidential experiences, as he socialized with and had the ear of a former president for two days in Houston at a gala event, an impromptu after-party at Tony’s, a Sunday brunch the next day at a River Oaks mansion and later aboard his plane.

“I think you can see a core of Trump in this,” said Barry Silverman, a Houston advertising and marketing consultant who helped coordinate the gala and was a longtime friend of the Connallys. “He obviously had a road map a lot bigger than any of us ever thought about.”