COSTA MESA, Calif. — Around 4 p.m. here on Monday, an aide to Mitt Romney, Garrett Jackson, showed the candidate a grainy video that had been circulating online all afternoon.

It was not pleasant viewing.

On a day freighted with symbolism and expectancy, the 50th until the election, Mr. Romney quietly watched himself deliver words at a fund-raiser — about the “47 percent,” “victims” and “dependents” — that would cast a new cloud over his campaign.

Mr. Romney and his advisers quickly grasped the severity of the footage, shot surreptitiously in Florida a few months ago and suddenly dominating the cable news airwaves and political blogs.

A decision was made: Mr. Romney must go in front of cameras that night to explain himself, lest questions about the video linger and overshadow two full days of his campaign at a crucial stage in the general election.

But there was little time. It was already 7 p.m. on the East Coast, after the evening newscasts, and Mr. Romney was scheduled to attend a major fund-raiser in Costa Mesa in a few hours.

So aides quickly began arranging an impromptu news conference, giving the journalists who travel with Mr. Romney just a few minutes to race over to the Segerstrom Center for the Arts, an elegant modern glass-and-steel building where he would hold the fund-raiser.

Reporters, who had expected a quiet evening, had already fanned out around town. As their phones began buzzing with urgent messages, they sprinted over to the arts center in whatever they were wearing (blue jean shorts, T-shirts), looking unkempt (one had just finished a run, but had not showered) and without their gear (in their rush, several left behind their laptops).

Well-dressed donors, sipping wine, stared at the journalists now traipsing through their event in confusion.

The location was less than ideal. Aides had commandeered a small ballroom at a fund-raiser to have Mr. Romney discuss embarrassing remarks he had made at, well, a previous fund-raiser.

Kevin Madden, Mr. Romney’s spokesman, peeked his head out from behind a black curtain, looking somewhat nervous. Around 10 p.m. Eastern time, Mr. Romney walked out, delivered his statement and took three questions.

Back inside the fund-raiser, Mr. Romney was running late. His longtime campaign finance chief, Spencer Zwick, apologized to donors for the delay, telling them that the candidate hated to be late and offering up a vague explanation.

“We had a press event that we had not anticipated we would do in the middle of a fund-raiser,” he told them. “But this is a presidential campaign and we don’t always get to predict what’s going to happen every single day.”