“Everyone was taken aback to discover just how extensive the operation had been,” said Anita Dunn, a former White House communications director under Mr. Obama and a partner in SKDKnickerbocker, a consulting firm advising Planned Parenthood on managing the crisis.

Ms. Dunn said Planned Parenthood had three immediate challenges: to answer the attack, to simultaneously query 67 affiliates about which ones had tissue programs or contacts with the abortion opponents and to reassure supporters and political allies.

The group, which once enjoyed bipartisan support, has relied almost solely on Democrats since abortion opponents gained sway over the Republican Party in the Reagan era. Its heft with Democrats flows from its grass-roots support, and willingness to spend freely on advertising and get-out-the-vote efforts in key states.

Upon the initial video’s release, the national office contacted Democratic campaign committees and emailed an alert to affiliates. The chief executive of Planned Parenthood in Ohio, Stephanie Kight, quickly staged conference calls “to make sure that neither my board nor my staff hears about this when they pick up the paper” — a moot instinct in the social media age. “Within an hour or two, people are saying: ‘Steph, have you seen this? I just saw it on Facebook.’ ”

“National is on it,” she assured them. “We need time to figure it out.”

Former Gov. Ted Strickland of Ohio, a Democrat campaigning to unseat Senator Rob Portman, a Republican, heard an initial news report about the video and, he said, “How credible is it?” It’s not, officials were already telling his aides, even as they sought information themselves.

But perhaps those caught most off guard were employees in several Western states who recognized the couple who had secretly filmed the videos as the purported biotechnology representatives asking to buy fetal tissue during earlier visits to their facilities. In Colorado, Planned Parenthood officials warned aides to Senator Michael Bennet, a supportive Democrat facing re-election, that a Denver clinic might be featured in a coming video. It was, two weeks later.

Ms. Laguens of Planned Parenthood acknowledged the difficulty of quickly rebutting attacks even as her group was gathering facts. But, she added: “I’m 100 percent sure we are not trafficking in baby parts. So I didn’t have any hesitation, and Cecile didn’t have any hesitation, in saying, ‘That’s not true.’ ”