The protesters at Donald Trump’s rally in Portland on Thursday had no idea that their silent gesture of opposition – each of them holding up a pocket-sized copy of the U.S. Constitution while the Republican presidential candidate spoke – would be so effective.

Images and videos of the protesters were picked up by media around the nation, including CNN, Time magazine, Slate, the Guardian and Politico, which made note of the contrast between the protesters’ wordless march as they were escorted by Trump’s security team out of Merrill Auditorium, blue booklets held aloft, with the heckles and boos of Trump’s supporters.

The pocket Constitution protest was organized by the Maine People’s Alliance, a liberal advocacy group that coordinated their actions as Trump spoke at the podium.

MPA members who talked about the protest said on Friday they couldn’t remember which of them first came up with the idea.

“It was sort of crowdsourced between a bunch of us at the Maine People’s Alliance and taken to our chapter members who wanted to do something,” said Andrew Francis, the group’s deputy communications director.

But even they were surprised at how many media outlets noted their gesture. Although over 100 people gathered at Portland City Hall and nearby Monument Square to protest Trump’s appearance in Maine – his third this year – it was the silent protest inside the auditorium that captured national attention, with Slate calling it “pure imagery.”

“We didn’t predict this,” said Maria Testa, an author from Portland who was accompanied at the rally by her two sons and who is a member of the MPA. “We just thought it was a good thing for our city and our state. We couldn’t have predicted how the nation would have picked it up.”

The pocket Constitution first drew attention as an image of protest against Trump during a speech at the Democratic National Convention last week by Khizr Khan, the father of Muslim American Army Capt. Humayun Khan, who was killed by a suicide bomber while serving in Iraq in 2004. Humayun Khan was posthumously awarded the Bronze Star and the Purple Heart.

The elder Khan used his speech to criticize Trump’s proposal to ban Muslims from entering the U.S. As Khan spoke, he drew his copy of the Constitution from his suit jacket and held it up, saying, “In this document, look for the words liberty and equal protection of law. Let me ask you: Have you even read the U.S. Constitution? I will gladly lend you my copy.”

Trump’s subsequent criticism of the Gold Star family triggered widespread condemnation from veterans groups, and both Republican and Democratic leaders.

Francis was surprised that the images of the MPA members holding their Constitutions at the rally were also picked up on social media by so many “random people and celebrities,” including the national ACLU and celebrity Bette Midler, who both tweeted about the incident.

“We were holding up the Constitution at a Trump rally,” said 19-year-old Julia Leslie, another of the protesters inside Merrill Auditorium. “We were using our First Amendment right. The fact that he was dismissive of us is pretty ironic.”

A native of the Bangor area, Leslie is living in Yarmouth between semesters at Wellesley College. This is her first time participating in a presidential election.

“I’ve never been in a news story that was covered nationally,” she said, “so it was pretty exciting.”