The Guardian said that Trump Jr told the audience that taking questions from the floor risked creating soundbites that leftwing social media posters would abuse and distort.
Guilfoyle told audience members that they were being rude, according to the Guardian.
Shortly thereafter, she and Trump Jr left the stage.
The fiasco pointed to a factional rift on the Trump-supporting conservative right that has been growing rapidly in recent weeks, particularly among "zoomers" – student-age activists. On one side are one of the sponsors of Trump Jr's book tour, Turning Point USA, a campus conservative group with a track record of bringing provocative rightwing speakers to liberal universities.
On the other side are far-right activists – often referred to as white supremacists and neo-Nazis, although many of them reject such labels – who believe in slamming the door on all immigrants, not just those who cross the border without documents, and who want an end to America's military and diplomatic engagement with the wider world.
Outside the lecture hall, several dozen protesters organised by the Los Angeles chapter of Refuse Fascism protested. The Los Angeles Times reports that protesters chanted "UCLA protects fascists" and "humanity first."
Andy Stein, a supporter of President Donald Trump, told the Times that he came to UCLA to listen to Trump Jr because he sees the son as a "chip off the old block" and admires his "feistiness."
- AP
