“Activists in the L.G.B.T. community mobilized a fast and fierce campaign that included a protest outside of the White House on Monday to say transgender people cannot be expunged from society, in response to an unreleased Trump administration memo that proposes a strict definition of gender based on a person’s genitalia at birth.

The existence of the draft memo, the administration’s latest effort to roll back the recognition and protection of transgender people under federal civil rights law, was reported by The New York Times on Sunday morning.

Within hours on Sunday, the hashtag #WontBeErased circulated on social media. By Sunday evening, a rally for transgender rights took place in New York; another took place on Monday in Washington.

Ms. Keisling said she and her staff woke up on Sunday to the news of the memo and quickly planned a response. The hashtag #WontBeErased felt appropriate to them. “What this feels like to transgender people is trying to make us invisible, trying to say that we don’t exist, trying to say that we are nothing,” she said.

The #WontBeErased hashtag took off on social media, as people posted photos of themselves or family members to show the faces of transgender people — who, they noted, would continue to exist regardless of the government’s definition of gender.

The American public is divided over whether it is possible for a person’s gender to differ from the sex they were assigned at birth, according to a Pew Research Center survey published last year, amid debates over which public bathrooms transgender people should use.

It said the divide was evident along political lines, with 80 percent of Republicans and Republican-leaning independents saying that whether someone is a man or a woman is determined by the sex they were assigned at birth. About 64 percent of Democrats or those who hold their views say a person’s gender can be different from the sex they were assigned at birth.”

Let’s show them we exist!! #WontBeErased