A young girl uses protest signs to build a wall while taking part in the Women’s March on Washington to protest Donald Trump’s inauguration as the 45th president of the United States close to the White House in Washington, Jan. 21, 2017. (REUTERS/Lucas Jackson)

With Donald Trump’s presidency has come the most visible eruption of popular protest in recent memory. On a range of issues — women’s liberties, immigrant and refugee rights, Trump’s tax returns, and more — protesters are hitting the streets, speaking out on social media, disrupting venues and events, and signing mass petitions. As of a week ago, the most popular petition on the White House website called for the release of the president’s tax returns, while a petition calling for banning Trump from Britain reached 1.3 million signatures.

Can petitions matter, though? A recent article in The Washington Post begins with the headline, “It turns out petitioning the White House is about as effective as asking Justin Bieber to deport himself.”

But perhaps the main effect of a petition is not persuading its target, but recruiting new people to a cause. Indeed, recruiting and not persuasion is sometimes the goal, not just the effect. Contrary to conventional wisdom, petitions can have a long-term organizational legacy even if their short-term policy effect is zero.

Signing a petition is a social act — and gives organizers your name and contact information 

The signature list is the key difference between petitions and other protest activities. When we sign petitions, our information becomes visible to others, including organizers and people who might sign later. Protesting is usually different, as you can march without signing something — although there is evidence that if you make a commitment (say, on Facebook) to a march ahead of time, others’ approval encourages you to get still more involved.

For the next possible joiner of a movement, seeing others’ names on a petition may encourage them to sign something controversial. And for organizers of new movements, someone’s signature (along with their email address or other information) shows a potential commitment to something beyond that petition — to joining a new group, to donating money, time or energy, to voting. The signature list becomes a database of potential recruits for activists.

For centuries, petitions have been successful recruiting tools for new movements

In recent research my colleagues and I have presented evidence for “recruitment by petition.” The eminent statesman Henry Clay understood this power of petitioning. In 1834, as Andrew Jackson was trying to shut down the Bank of the United States, Clay asked Bank supporters to launch a petitioning campaign to save it. As the campaign wore on, the pro-Bank petitions turned into anti-Jackson petitions, which Clay encouraged. More than 100,000 Americans signed the anti-Jackson petitions. In the counties where they signed most heavily, the Whig Party was born two to eight years later.

In the 1830s, Congress enacted a “gag rule” on slavery-related petitions. Petitions were supposed to be read on the floor of Congress, but these legislators refused to do that. All antislavery petitions were tabled without a hearing and without being referred to a working committee.

And yet in the months after the rule passed, antislavery petitioning exploded to heights unparalleled in American history. Per capita, more petitions were sent to Congress in 1837 to 1839 than ever before or ever since. Activity surged most heavily among young women who had never been involved in politics before. These women not only signed in much greater numbers, they also canvassed petitions with amazing energy, getting far more signatures than men did. A few years later, new antislavery chapters and parties started exactly where petitions had been signed a few years earlier.

This recruitment pattern is quite old. As I have described elsewhere, and as the historian Allan Tulchin narrates in an excellent book, Protestants in 16th-century France used a form of petition to attract new converts, even though it was clear that the French king was unlikely to respond favorably. And in the English Civil War, the king’s opponents used petitions to organize — so much so that after the monarchy was restored, Parliament passed a law in 1662 saying that only 20 names were allowed on any petition, in order to prevent the accumulation of names from escalating into new movements.

Can petitions be used to recruit today?

Quite possibly. Some evidence suggests that, in the United States, non-voters who sign new, popular petitions are later more likely to vote. Political scientist David Karpf has studied online mobilization and observes that activists think some petitions are better than others for mobilizing action. Activists phrase some petitions to touch upon an issue (corruption, or an unpopular leader or war) that can bring otherwise reluctant people out of their political inactivity. So phrasing matters, but so does political context: The issues have to matter to people in a way they didn’t before.

Political organizers also recognize the power of the signatory list and use the contact information contained in petitions to recruit. When you sign a petition online, your email address goes into a database that that organization, or others, will almost certainly use to ask you to sign another, to give money, to volunteer and possibly later to vote.

There’s a downside to online petitions, though. Their signatures aren’t gathered during face-to-face conversation. That reduces some of the networking opportunities that make paper petitions powerful. Political scientist Hahrie Han finds that mobilizing (including petition signing) is more effective at encouraging participation when there is a “relational context,” by which she means a sense of belonging to a group. Online petitions probably offer less of that than paper ones do.

One study suggests that signing something electronically inspires less emotional commitment to a cause than signing by hand. Petitions sent to the White House might be the least effective kind: They are started on a White House website, the signature data stay there (making that data more difficult for activists to use), and signatures aren’t gathered face to face.

Nevertheless, studies of electronic petitions have found that signing them can be a transition from merely “lurking” to getting active in other forms of political participation, such as donating, protesting and voting. Signing a petition can enhance the citizen’s sense of efficacy, spurring more interest in politics and connecting them to others. The Obama administration launched the White House petition site based on one started by the British prime minister for Parliament. Scholars who have studied that British model do find that signing those petitions does tend to get people more politically involved.

So petitions do make a difference — in the people who sign them

Whether or not Justin Bieber deports himself, and whether or not Trump responds to those White House petitions, those petitions do matter. While they may not have an effect now on policy, they are likely to have an effect later, on politics.

When you’re looking at a petition, you may be seeing an opposition movement being organized before your eyes.

Daniel Carpenter is a professor of government and Director of Social Sciences at the Radcliffe Institute for Advanced Study at Harvard. You can find his petitions project here.