Some pantsuits were white, in tribute to the dresses of the suffragists. Others were mismatched or borrowed. Many were fished out of the back of a closet, along with a memory of a long-lost job or a somber occasion.

These suits were redeployed by thousands of American women on Election Day, when taking a photo of yourself in a pantsuit and posting it to the “secret” Facebook group Pantsuit Nation became the digital equivalent of slapping an “I Voted” sticker on a lapel.

“They’re coming in at about 1,000 every few minutes,” Libby Chamberlain, the founder of the group, said of the social media posts. “We have over 20,000 posts that are waiting to be approved. We have dozens of moderators and they can’t keep up.”

“It’s intense,” she added.

Ms. Chamberlain, 33, created Pantsuit Nation to support Hillary Clinton, the Democratic presidential nominee, less than three weeks ago. Since then, more than 2.5 million people have joined the group — which is invitation only — and have reported donating more than $216,000 through the Pantsuit Nation fund-raising drive. But even that growth didn’t prepare the group’s organizers for the explosive activity on Tuesday.