Mr. Trump’s campaign did not respond to questions about its social media director’s gibe at Mr. Ryan, which at a minimum showed a lack of message discipline inside the campaign. Whether it would endanger Mr. Ryan’s support of Mr. Trump was not clear; the speaker’s office did not respond to requests for comment Saturday.

He was forced to respond Friday when pressed by Ms. Brown, who now runs an education website and is married to Dan Senor, who was an adviser to Mr. Ryan and to one of Mr. Trump’s primary race rivals, Senator Marco Rubio of Florida.

Turning to Mr. Ryan during a panel discussion, Ms. Brown told him that one morning, one of her sons, expressing disappointment, had asked why he endorsed Mr. Trump.

What, she asked Mr. Ryan, was she supposed to tell her child?

The attendee present for the exchange said Mr. Ryan appeared slightly uncomfortable but handled the question well. He said Mr. Ryan had explained that while he understood the disagreement among Republicans, he believed that his decision to support Mr. Trump would be better for the Republican Party in the long term.