"She posed the question, 'Is it not reasonable to support Hillary Clinton?' given all the awful things Trump has said," explained donor John Chachas.
Whitman served as Romney's finance co-chair in 2012.
But asked if she was switching over to the other side, Whitman told ABC News, "I haven't made that decision. We’ll see, get to the conventions, see who the vice presidential picks are. And then I will make that decision." Her office declined to comment further when asked.
Whitman's words come as a majority of Romney loyalists -- many of whom spearheaded the "Never Trump" movement -- are facing tough decisions about who to back this cycle. Romney himself has been one of Trump's most outspoken critics, and has openly declared he would not be voting for the presumptive GOP presidential candidate.
"These guys are a lot smarter than I am, and if they’re endorsing [Trump], that's kind of reassuring to me,” said Scott Keller, a donor from Utah who was at the summit and has decided to back Trump. Whitman, meanwhile, indicated she would likely vote for Clinton, but made no mention of actually donating to the presumptive Democratic presidential nominee. Still, some prominent Republican donors here were in shock.
"I see Meg Whitman supporting Clinton, and I’m surprised about that. I love and respect Meg Whitman but, my gosh," said Keller.
Keller added, however, that the "right thing" to do is to go vote for someone. Keller said that’s why he's planning to back Trump -- although he was reluctant to do so initially.
Ryan responded by saying he had party obligations as speaker of the House of Representatives, said the sources inside the room.
According to long-time Romney confidante, Spencer Zwick, Ryan was asked about his recent endorsement of Trump during his own speech at the summit but "said nothing new."
"He mostly talked about his agenda," Zwick said, adding: "I think a lot of people, they're tired talking about Trump University. They want to talk about policy and a path forward."
Whitman has previously gone on the record saying she wouldn't be voting for Trump.
"Look at the comments he's made about women, about Muslims, about reporters, it's just repugnant," she told CNBC in March.
According to Jim and Joanne, a couple from Southern California who declined to provide their last names, Whitman isn't the only donor here considering Clinton. The summit attendees took an informal poll at lunch, with the room splitting evenly among Trump and Clinton supporters, they said.