Only weeks into the administration of President Trump, many residents of this heavily Democratic area who once attended the occasional protest have adopted resistance to the Trump administration as a lifestyle. They go to weekend marches, organize with friends after work or get together to send batches of postcards to the White House.

“I did notice that it’s getting to be more of a type of social event,” said Denisha Jones, an assistant professor of teacher education at Trinity Washington University, who has attended several protests since Inauguration Day. “Folks I normally go to brunch with, we go to protests.”

“Protesting is the new brunch” sounds like an inscription on a T-shirt — and, thanks to the internet, it is. But it’s also a phrase traded among friends at bars, at work or on the walk home from yet another demonstration. “See you next weekend,” people say.

Sometimes it’s even sooner than that. Protests organized against Mr. Trump can amass hundreds on the fly: When the administration issued its first version of a travel ban that barred people from seven predominantly Muslim nations, Ms. Jones said, “the next day we were all at the White House.”