"These things are personal. I love this country. I love the founders, I love what this country is built upon and its values, and seeing this is breaking my heart, for the party that means so much," said Romney, choking up and blinking back tears.
Still, Romney insisted he understood those that have decided to back the presumptive Republican nominee, and said that he wouldn't be spending the next six months trying to convince anyone not to vote for Trump.
"I really understand both points of view about the pro- and contra-Trump setting, and respect people on both sides of this," he said.
"Both [Clinton and Trump] are destructive. I think that's the frustration many people in this room and many people around the country feel," he went on.
Asked why he had reached out to Trump for his endorsement when he was running for president in 2012, Romney replied that at that time Trump hadn't said the things he said this cycle. Trump’s focus on "birtherism" -- questioning President Obama's birthplace -- back then was "nutty" but not xenophobic, racist, or misogynist.
Romney also condemned the other GOP candidates this cycle for failing to take Trump on sooner.
He criticized Texas Sen. Ted Cruz for praising Trump until he realized that wasn’t working, Jeb Bush and his super PAC for spending so much money attacking people other than the frontrunner, and Ohio Gov. John Kasich for staying in the race too long.
"I think their biggest failure was not focusing on the frontrunner, and instead focusing on each other," he said.
Still, he conceded that Trump "won fair and square" and had a "very effective strategy" that capitalized on people's anger and frustration.