At the moderate pace of about 12.5 miles per day, a new crisis is slowly unfolding in Turkey. For almost three weeks, the previously uninspiring leader of the country’s main opposition party, the Republican People’s Party (CHP), has been walking from Ankara to Istanbul. As the “March for Justice,” which now includes thousands of supporters, wends its way toward Istanbul this week, it puts President Recep Tayyip Erdogan in one of the most precarious political positions of his 15 years in power. Unlike last summer’s failed coup, which few Turks supported, the march seems to have resonated with a wide constituency. The demand for justice also happens to be a core principle of Erdogan’s political party, aptly called “Justice and Development.” The march puts Erdogan in a bind: He can try to stop it, risking violence, or he can let it go on and watch the already large procession of opposition grow. Whatever Erdogan decides, the march makes it clear that he is weaker than he seems and that Turkey is becoming less, not more, stable under his authoritarian rule.

The March for Justice is a surprising stroke of genius for Kemal Kilicdaroglu, who, since rising to the leadership of his party in 2010, has been widely perceived as gentlemanly and well-meaning, but incompetent. The heretofore easily ignored CHP leader is, for the first time in his political career, defining events rather than responding to them. The stated reason for Kilicdaroglu to embark on his walk was the sentencing of a legislator from his own party, Enis Berberoglu, to 25 years in prison. Berberoglu, also a journalist, allegedly divulged state secrets about arms shipments to Islamist militants in Syria.

His conviction, however, is more catalyst than cause. It comes against the backdrop of a constitutional referendum on April 16, the fairness of which international observers have called into question, and a purge that has resulted in some 50,000 arrests, more than 100,000 detentions, hundreds of thousands more summarily dismissed from their jobs, and billions of dollars of property confiscated by the government, all in the last year. Kilicdaroglu has belatedly come to recognize that his previous efforts to block the president and his ruling Justice and Development Party (AKP) through parliamentary maneuvers were a fool’s errand.

The victory of the “yes” campaign in the April referendum was a major victory for Erdogan. As a result, Turkey’s new system enhances the power of the president at the expense of parliamentarians whose role overseeing the government is greatly diminished. The referendum also weakened another check on executive power by giving the president far greater control over the already highly politicized judicial system. The constitutional changes facilitate effective one-man rule and could allow Erdogan to remain in office until 2029, or even, according to some readings of the law, until 2034.

Yet the conduct and outcome of the referendum actually underline the softening of support for Erdogan and his party. Supported by the now almost universally pro-government press, the massive “yes” campaign also benefitted from the harassment of opponents , the disenfranchisement of hundreds of thousands of Kurdish voters, and vote rigging, yet only managed to produce a narrow margin of victory for Erdogan. He emerged from April’s referendum with vast institutional powers, but the outcome also evinced a new brittleness in his command of Turkey’s political arena.

The March for Justice highlights this weakness. As it approaches the outskirts of Istanbul — Turkey’s largest population center, a traditional AKP stronghold and Erdogan’s hometown where he once served as mayor — the march is demonstrating that resistance to Erdogan remains possible and that the opposition remains broad. Kilicdaroglu’s effort has brought together an unlikely, if uneasy, alliance of his own party, pro-Kurdish rights groups, and hard-line Turkish nationalists. Should the march reach Istanbul, it could conceivably gather hundreds of thousands of supporters and spark “sympathy rallies” elsewhere.

Based on past precedent, it seems unlikely that Erdogan will be willing to tolerate such a train of events. In summer 2013, when protests over the planned redevelopment of a small park in central Istanbul turned into large-scale anti-government demonstrations across the country, Erdogan ordered the riot police to take a hard line. Thousands of protesters were treated to tear gas, water cannons, beatings, and arrests while Erdogan called on the party faithful to turn out in even larger numbers to demonstrate their support for him and the AKP. Since the Gezi Park protests, the government has not allowed large-scale anti-government demonstrations. Even Istanbul’s Pride March, which the AKP once pointed to as a demonstration of its liberalism, is now suppressed with water cannons and rubber bullets. The government has become remarkably adept at limiting the size of protests by pouring thousands of police into the streets, preventing access to protest sites and limiting the protesters’ capacity to unite. Through all of this, Erdogan has yet to suffer politically from unleashing the full force of the police.

The temptation for the government to suppress the March for Justice is thus likely strong, but such a course also carries significant risk. Stopping the marchers by blocking the road would result in an ugly stand-off that would draw international media attention to an underreported story. If Kilicdaroglu is allowed to position himself even more effectively as a principled, peaceful democrat, the story would dominate the news cycle on relatively favorable terms as long as the stand-off lasted – even in a media environment very friendly to the AKP. Removing police protection from the march, another way of short-circuiting the protest, would give Erdogan’s supporters a free hand to bully and physically harass the marchers. This would almost certainly lead to broad civil unrest.

Erdogan wants to stop the march, but he also benefits from the illusion that Turkey is a functioning democracy. Banning the march and detaining Kilicdaroglu and other CHP leaders would further undermine this pretense. This does not seem like it would be much of an issue for a leader who has overseen the deepening of authoritarian politics, but an important element of Erdogan’s success is that he can claim to be democratic and to fairly represent the popular will. The opposition does not believe this, but it is critical to Erdogan’s legitimacy that his own base does. The unfairness of the referendum combined with the ever-expanding purge may have forced some within the AKP to think twice about concentrating so much power in Erdogan’s hands. Almost all were willing to accept the jailing of the pro-Kurdish politicians as part of the country’s fight with the PKK, but an open attack on Kilicdaroglu would represent a significant escalation even for Erdogan’s own party. The AKP may have laid the groundwork for this when members of the party’s leadership, including the prime minister, recently implied that Kilicdaroglu is either a terrorist or enjoys the support of terrorists. Still, while most of his supporters are willing to accept Erdogan as a populist strongman, fewer will likely accept him as an open dictator.

With the March for Justice, Kilicdaroglu has finally found a way to put Erdogan and the AKP on the defensive. The march is supposed to conclude in Istanbul on July 9, although the blistering summer heat has slowed its progress. This timing creates a particular challenge for Erdogan because of its proximity to the first anniversary of the attempted coup of July 15, 2016 — a date that has become central to his own narrative of himself as the democratic embodiment of Turkey’s national will. Instead of the massive outpouring of support that he no doubt expects, Erdogan may find himself confronting throngs of peaceful protesters angered that he has driven the country so far from its, and his, own stated democratic principles. It is precisely this growing gap between what governments tell their people about their lives and the way citizens actually experience reality that has proven politically fatal for leaders like Egypt’s Hosni Mubarak in the recent past. No one expects Erdogan to meet a similar fate, but if he wants to avoid further political polarization and the instability that comes with it, permitting Kilicdaroglu to finish his march is the safer option. It is more consistent with Erdogan’s claims about Turkish democracy — incredulous though they may be to his opponents — and, importantly, will avoid bloodshed.

From the outside, Erdogan may look like the master of his domain, leading a strong and prosperous country. But the March for Justice has laid bare another reality. Along with the events of three of the four previous summers — the Gezi Park protests, renewed war with the PKK, the failed coup — the march reveals a deeply divided, authoritarian, and unstable country. If Erdogan chooses poorly this summer, Turkey may become more unstable and dictatorial yet.

Howard Eissenstat is an Associate Professor of History at St. Lawrence University and a Nonresident Senior Fellow at the Project on Middle East Democracy (POMED). Steven A. Cook is the Eni Enrico Mattei Senior Fellow for Middle East and Africa Studies at the Council on Foreign Relations. His new book, False Dawn: Protest, Democracy, and Violence in the New Middle East, was published by Oxford University Press in June.