Paul Ryan, left, and Mitt Romney campaign together in 2012. (Melina Mara/The Washington Post)

PARK CITY, Utah — House Speaker Paul D. Ryan (R-Wis.) faced tough questioning here Friday for his decision to endorse Donald Trump, and he tried to explain to an audience hostile to the New York mogul the factors that led him to back the presumptive GOP nominee.

Ryan’s appearance briefly brought into the open the issue that has shadowed the annual ideas summit hosted by 2012 GOP nominee Mitt Romney — the alarm with which many establishment Republicans view Trump’s pending nomination and the potential damage it could do to the party in November and beyond.

Ryan's closed-door session — attended by about 300 elite Republican donors and business executives — also highlighted his differences with his friend and ally, Romney, who tapped him as his vice-presidential running mate and is now an avowed leader of the Never Trump movement.

Campbell Brown, a former CNN anchor and founder of the education news site the74.org, moderated the session with Ryan and grilled him about his decision. She told him that her young son, who knows and admires Ryan, came into the bedroom the morning after he had announced his support for Trump dismayed by the news.

How would you explain this to a child? Brown asked Ryan. The speaker appeared uncomfortable.

House Speaker Paul Ryan (R-Wis.) criticized Donald Trump June 7, for remarks Trump made about a Latino federal judge. However, Ryan said Trump is still a better alternative to Democratic presidential candidate Hillary Clinton. (Reuters)

Reporters were excluded from the off-the-record session, but the exchanges were described later by three people in the room spoke on the condition of anonymity in order to share what had happened.

One of the toughest questions for Ryan came from Meg Whitman, the chief executive of Hewlett-Packard and a longtime friend of Romney's who helped bankroll a Republican anti-Trump super PAC this spring. Whitman asked Ryan how he could endorse someone with, in her judgment, such poor character and whose campaign has been based on personal attacks and division. According to two people present, Whitman said Trump is the latest in a long line of historic demagogues, explicitly comparing him to Adolf Hitler and Benito Mussolini.

Ryan explained the difficult political situation he was in, as the leader of House Republicans. While spending a couple of weeks last month deliberating about an endorsement, many of his members increased pressure on him to back Trump. Many of them represent districts where Republican voters are strongly supportive of Trump, Ryan explained.

Ryan spent part of his appearance promoting his agenda for House Republicans, including a robust discussion of national security and efforts to eliminate poverty.

The audience was described as largely anti-Trump yet sympathetic to Ryan's predicament. Many are supportive of Ryan and have been for years.

One attendee stood up to plead with Ryan, "Will you please run for president in 2020?" The room erupted in applause. That assumes, of course, that Trump is not the incumbent president getting ready to run for reelection.