CAIRO -- Two months ago, five young activists at a Cairo coffee shop hatched a simple plot to capture the growing public frustration with the direction of their country: collect signatures calling for the ouster of President Mohamed Morsi and organize a protest at the presidential palace on June 30, the anniversary of his inauguration.
As happened once before, with the demonstrations that toppled the former president, Hosni Mubarak, the results ran far beyond the organizers' expectations.
The campaign, called "tamarrod," Arabic for "rebellion," spawned branches across the country and rallied millions of Egyptians to join the protests this weekend that have infuriated the country's Islamists, shaken Mr. Morsi's grip on power and pushed the Egyptian military to threaten to once again take over the country.
The campaign's success has made its originators -- Mahmoud Badr, Mohammed Abdel-Aziz, Hassan Shahin, Mai Wahba and Mohammed Heikal, all 22 to 30 years old -- heroes to those who oppose the Muslim Brotherhood. They are cheered at protests, hounded by journalists and sought after as guests on evening talk shows.
Their movement, however, underlines both the greatest strengths and the most glaring weaknesses of the youth groups that have driven many of Egypt's most fundamental political transformations since the revolution, channeling public sentiment to political change but failing to transform it into sustainable organizations.
"While they are communicating for the people, they are not figuring out how to organize people within the political process itself other than calling on them to protest," said Rabab el-Mahdi, a professor of political science at the American University in Cairo. Dr. Mahdi said that the group's lack of a well-articulated political project likely means it will "vanish just like other youth coalitions because they are about what they don't want, not about what they want."
The tamarrod campaign was born in late April among five friends who had gotten to know each other through another political movement that eventually helped bring down Mr. Mubarak in February 2011. They all work in opposition news media, but have distanced themselves from political parties. They are all Muslims and personally devout, but deeply distrustful of the political Islamism of the Muslim Brotherhood.
After the uprising that pushed Mr. Mubarak from power, they came to believe that the revolution had gone off track, and especially that Mr. Morsi, the country's first freely elected president, had failed to transcend his roots in the Muslim Brotherhood, which had dominated post-revolutionary elections.
"The idea at the start was that there was lots of anger in the street against the Brotherhood and Morsi, and that one part of society had taken over the government and not carried out any reforms that have benefited people," said Mr. Shahin, 22, who is credited with suggesting the campaign to his friends.
The group created a simple petition to withdraw confidence from Mr. Morsi and call for early presidential elections. They spread the idea on Facebook and Twitter and started collecting signatures in Tahrir Square during Labor Day protests on May 1.
Mr. Badr, one of the organizers, said the group was amazed at the response and collected thousands of signatures that day, so many that they ran out of petitions and had to make more copies.
They later had friends outside Cairo help collect signatures around the country. Soon, groups they had never heard of had joined the campaign and were gathering signatures on their own and delivering stacks of signed petitions to the group's downtown Cairo headquarters.
Since its start, the campaign has remained ideologically neutral, saying only that it supports a democracy that all Egyptians can participate in. It was only after word of it spread that prominent opposition figures like Mohamed ElBaradei and a former presidential candidate, Hamdeen Sabahi, established ties.
"This is the voice of the Egyptian people, and we would commit a historical error if we turned it into a political party," said Ms. Wahba, the founding group's only woman. "This is the completion of the revolution."
The campaign's popularity spread by tapping into widening discontent over the state of the country. As the economy continued to sink at the start of the summer and power outages and gas shortages became more common, many Egyptians blamed Mr. Morsi.
Others accused him of trying to "Brotherhoodize" the state by appointing Brotherhood members and other Islamists to key government positions.
As Sunday's protests approached, tamarrod campaigners were often seen on main thoroughfares, sometimes stopping cars with huge signs reading "Leave!" and collecting signatures. In some provinces, they clashed with Brotherhood members.
The group said it had collected 22 million signatures, an assertion that is impossible to verify. After Sunday's protests, however, they gave up on vague plans to ask the United Nations to verify the signatures by pointing to the masses of demonstrators.
"Those signatures have turned into the crowds of citizens that you see in the public squares across the country," Mr. Badr said.
The campaign has infuriated Mr. Morsi's supporters, who launched a rival petition campaign called "tagarrod" -- "impartiality" -- and organized their own mass demonstration in Cairo to support Mr. Morsi.
Islamist speakers at the pro-Morsi rally have dismissed opponents as the tools of pro-Mubarak figures who want to regain power and accused them of being anti-Islam. Others call the campaign anti-democratic for demanding an early end to Mr. Morsi's elected four-year term.
"If the opposition really has the ability to bring out millions of protesters and collect millions of signatures, why can't they get all of those people to vote in elections?" said Tamer Abdel-Maqsoud, a Muslim Brotherhood protester. "We are trying to build the institutions of the state, and this will never happen if the politics of thuggery get rid of the first elected president."
Hala Mustafa, a political analyst and writer, said the campaign's success only highlighted the formal opposition's failure to establish a popular base. "The opposition needs more integrity and more work on the ground," she said. "It is not enough to be on television 24 hours a day and make a big show."
Tamarrod's organizers acknowledge that they have no political program, but say it is up to Egyptians to decide what comes next if Mr. Morsi is toppled.
"In only two months we made this huge accomplishment and people also expect us to create a party program?" said Mr. Badr. "That's crazy."
Now, however, they are relishing their surprising success. Mr. Badr said that when he arrived at the protest in front of the presidential palace on Sunday night, people recognized him, lifted him off his feet and carried him to the stage, where he addressed the crowd.
"Everyone was telling us that we don't trust this party or that party," he said. "We trust only you."
Correction: July 2, 2013, Tuesday
This article has been revised to reflect the following correction: An earlier version of this article misspelled the given name of a former presidential candidate in Egypt. He is Hamdeen Sabahi, not Hamden.
This article originally appeared in The New York Times.