In quiet coffee shops, bookstores, and Unitarian Universalist churches, the liberals are gathering, armed with the antiquated tools of an emerging resistance: markers, cards, and postage stamps.

They are joining up for postcard-writing parties, elaborately illustrating and then sharing their handiwork on social media in preparation for Wednesday, the Ides of March.

Beware.

A president whose preferred mode of communication is a 140-character tweet is about to receive a deluge of opposition the old-fashioned way: via snail mail. Dubbed the “Ides of Trump,’’ the movement aims to inundate President Trump with postcards and to set a postal record: 1 million pieces of mail to one person in a single day.

Why, you might ask?

Chiefly, to annoy him.

“And we, in vast numbers, from all corners of the world, will overwhelm Washington with the president’s unpopularity and our negative opinions of his agenda,’’ the group’s Facebook page proclaims.

“Obviously, numbers matter a lot to him,’’ said Leslie Evans, an artist and printmaker who produced about 900 postcards for a party last week in Watertown. She pointed to the president’s devotion to his poll numbers and his false claim that the crowd assembled for his inauguration was larger than Barack Obama’s audiences. “He likes people to like him.’’

Many want to assure him they do not, and they have been sending postcards to the White House since the inauguration. Sometimes snarky, sometimes angry, the postcards’ messages target their outrage of the day or the hour. “Something’s fishy with you and Russia,’’ a Michigan woman wrote last week on a postcard that featured a picture of salmon. “Didn’t need a wiretap to know this.’’

The messages Evans printed on letterpress for the postcard party at First Parish Watertown featured rhymes that might be chanted at protest: “Compassion, not fear, Immigrants are Welcome Here,’’ and “Hear our voice, you are not the majority choice.’’

The old-fashioned medium for conveying those slogans seemed to stump some.

“A lot of people these days don’t even know how to address a postcard,’’ said Eileen Ryan, a Watertown woman who organized the event. “I made a sample postcard after I had people kind of botch it.’’

Maybe, she said, they thought she was going to send them in an envelope.

If this seems to be a counterintuitive way to communicate in today’s world, so be it. The guy who dreamed it up wanted the messages to be tangible.

Zack Kushner, a 44-year-old Sudbury native and freelance copywriter who lives in California, was overwhelmed by the turnout at the women’s march in Oakland in January. The trains were overcrowded; his 2-year-old lost a boot. They could barely get near the center of action, but they wanted their voices heard.

“What if everyone could be counted another way?’’ he wondered. An online petition or Facebook page doesn’t hold the weight of a physical object, Kushner said.

“That somebody took the time to write something, get a stamp, put it in the mail — there’s an additional level of commitment and resistance,’’ he said.

This being 2017, the postcards are highlighted on Facebook pages and Twitter feeds whose creators hope they are building a network of activists who will get involved in other ways.

Sydne Didier, 46, of Amherst, has been sending seven to 10 postcards a day and created a “Letters to Donald’’ Facebook page that has seen an influx of outrage from postcard writers from San Francisco to Pennsylvania.

She harbors no illusions, though, that her stellar penmanship and clever messages will reach the president.

“I don’t know what happens when they’re received,’’ she said. “But in my mind, I have this image of someone in the mailroom having a laugh.’’

All presidents receive a sampling of their mail, said Desiree Thompson Sayle, who heads Trump’s White House Office of Presidential Correspondence and who worked there under former president George W. Bush.

Obama tried to read 10 letters a day from the 10,000 or so he received, according to The New York Times Magazine. Selections were curated by a staff of 50, plus 36 interns and volunteers.

Sayle could not immediately detail how the process plays out under the Trump administration but said “every president wants to be very much in touch with the American people.’’

The postcard writers hope their message also comes from their abundance. And their medium, meanwhile, provides cheap therapy.

Regan Hall, a Greenfield mother and artist, described herself as “despondent, not sleeping, really angry’’ after the November election, and her calls to the White House comment line weren’t going through. After Didier introduced her to the “Letters to Donald’’ Facebook page, Hall began to channel that energy into art.

Her series of presidential postcards, meticulous sketches of former presidents, includes messages she’d like each of them to convey to the current president. On any given day, “they could give him little tips or pointers or berate him for killing the EPA,’’ she said.

“I started with Richard Nixon and had this epiphany like I could do all of these guys and it would focus me,’’ Hall said. “It’s meditative.’’

When she ran out of presidents, she rolled into a series of notable women in history, from environmentalist Rachel Carson to Frances Perkins, the first woman to serve as Cabinet secretary.

As history goes, of course, the Ides of March casts a dark shadow. The March 15 date is known for the assassination of Julius Caesar in a conspiracy by Roman senators wary of the growing power of the man who had just become “dictator for life.’’ In Shakespeare’s play, “Beware the Ides of March,’’ is the ominous message of a soothsayer.

Kushner — who is no known relation to the president’s son-in-law Jared Kushner, by the way — added an all-caps caveat on his website, saying his only rule is no threats of violence. “We understand that the Ides of March has a history, but that’s not what we are — in any way — calling for here,’’ he wrote.

“If we could cause Donald Trump to have a bad day, I would feel good about that,’’ he added. “But I don’t even need to give him an ulcer.’’

Stephanie Ebbert can be reached at Stephanie.Ebbert@globe.com. Follow her on Twitter @StephanieEbbert