"This was a hard-fought campaign. That's what made it so exciting and intense and why people's passions ran so high on both sides. I know my supporters have extremely strong feelings and I know Barack's do as well," Clinton said. "But we are a family and we have an opportunity now to really demonstrate clearly we do know what's at stake, and we will do whatever it takes to win back this White House."
Obama complimented Clinton on a hard-fought race acknowledging loyalties remained and harmony might not come easy.
"I recognize that this room shared the same passion that a roomful of my supporters would show. I do not expect that passion to be transferred. Senator Clinton is unique, and your relationships with her are unique."
But he added, "Senator Clinton and I at our core agree deeply that this country needs to change."
Clinton and Obama were warmly received by the crowd, but several attendees said they couldn't help but feel tension, even while they were likely to play supportive roles in Obama's race against presumptive Republican nominee Sen. John McCain of Arizona.
One major Clinton donor described it as an uncomfortable family visit.
"This felt like when your mom forces you to go visit your Aunt Ida and she has to pinch your cheeks and you're sitting there in an uncomfortable suit and you can't wait to leave," the donor said.
Another Clinton-leaning person who was in the room said after the meeting wrapped up that there is still "a lot of anger" toward Obama among the New York senator's wealthiest fans.
"It was pretty bad," the source said. He said donors were joking that the scene was like "an Irish wake" and that you "could cut the air with a knife" it was so tense in the room.
The former rivals showed solidarity and then Obama showed Clinton the money, pledging to use his fundraisers to help retire some of Clinton's more than $10 million in debts. That vow drew a standing ovation from the crowd.
He and his finance chair gave Clinton's campaign chair, Terry McAuliffe, personal checks.
Of the dollar amounts, McAuliffe said "They maxed out."
The meeting was a step towards reconciliation, but the wrangling over just how much Obama will help Clinton with her debt is not over. And Bill Clinton's quiet shadow looms. The former president has yet to say one word of praise for the man who beat his wife.
Many Clinton donors are anxious to hear more about Clinton's future role in Obama's campaign, at the Democratic convention in August and whether her delegates will be allowed any kind of symbolic vote on the convention floor.
Asked Thursday night if there would be a roll call vote at the convention in Denver, Clinton and Obama exchanged glances, with Clinton smiling, and said that was still being negotiated.
ABC News' Jennifer Duck contributed to this report.