In the eighty-four-year history of Egypt’s Muslim Brotherhood, there have been few weeks more remarkable than the past four. A movement born in resistance to British colonialism, and which later thrived protesting against secular dictatorships, is grappling now with the dilemmas of seizing and holding national power, as the whole world looks on in a state of tightening anxiety.

The spectacle is riveting because the political future of Egypt, the Arab world’s most populous nation, hangs in the balance. It is fascinating, too, because it is a kind of proving ground for long-running debates about whether an Islamist revolutionary movement such as the Brotherhood can ever adapt itself to Western-style constitutional democracy, preserving the rights of minorities and space for individual conscience.

Cairo this week seems a little like St. Petersburg in 1917: A revolution long incubated by clandestine organizers—some of them radical and violent, others more pragmatic and accommodating—may be defining itself for the longer run. Is the Muslim Brotherhood an Islamist party within a larger Egyptian nationalist and democratic front, one that includes Christians and secularists? Is it capable of sharing authority and building consensus with its opponents? Or will it only act opportunistically to secure its own control over the country and enforce the Islamic principles at the center of its ideology, leading it to pursue a form of religious dictatorship?

The contest now taking place among the Brotherhood, the Egyptian military, the country’s minority Christian Copts, and secular democratic parties could hardly be more complicated. There is fault and fracture on all sides. At the moment, the biggest question—a marker of the Brotherhood’s intentions—is whether President Mohamed Morsi, a member of the Brotherhood, will delay or amend a referendum on a draft constitution hastily created by a Brotherhood-dominated assembly. (For now, the voting is scheduled for December 15th, with some dispute over whether there will be a second day of voting on the 22nd.) A delay could allow for renewed negotiations with the secular-leaning opposition to create a draft that both sides would support.

The Brotherhood’s decision to jam through a constitution has coincided with other disturbing acts. Egyptian editors and broadcasting executives complain that the Brotherhood’s censorship practices are now worse than those of the former dictator Hosni Mubarak. Morsi has also sought to usurp the judiciary by decree, although he partially backed down. In each of these cases, the Brotherhood has offered excuses that have some basis in fact, namely that there are many holdovers from the Mubarak machine in the judiciary and the media who are out to undermine the Brotherhood’s legitimate electoral mandate. Yet the Brotherhood’s explanations are increasingly sound tinged with paranoia and authoritarian arrogance—and the movement has dispatched violent cadres to beat up peaceful opposition protesters. This is the question that has shadowed the revolution from the beginning: Can the Muslim Brotherhood be trusted?

Hassan al-Banna, an Egyptian schoolteacher, founded the Brotherhood in 1928. His goal was to restore economic and political power to the Islamic world by creating governments grounded in conservative Islamic principles. Although it started in Egypt, the Brotherhood established branches worldwide—there are Brotherhood-influenced movements and political parties in most of the world’s Muslim majority nations, from Asia to the oil-rich Gulf States to North Africa. Their record as democratic participants is mixed. Muslim Brothers have sat in Kuwait’s peaceable, noisy, constrained parliament, and they have evolved into a passive if restive opposition in Jordan. The Brotherhood’s Pakistani offshoot, Jamaat-e-Islami, functions as a fairly normal political party; it competes in elections, has a form of internal democracy, and has shared power in governing coalitions. Yet, like the Egyptian Brotherhood, in the past Jamaat-e-Islami has supported armed wings that have carried out terrorist attacks and other ruthless violence.

Hamas, the Brotherhood’s Palestinian branch, forged by years of conflict with both Israel and the secular Palestinian Authority, is a violent militia that carries out indiscriminate violence against Israeli civilians. Yet it is also a political movement that runs hospitals and universities in Gaza and maintains sophisticated political liaisons with a number of governments, Arab and otherwise.

One of the Brotherhood’s distinctive characteristics is its clandestine, one-on-one recruiting of members, particularly of young men who belong to the social and economic élite. (Osama bin Laden was recruited at his high school in Jeddah, Saudi Arabia, by his Syrian-born physical-education teacher, but later broke with the Brotherhood, finding it too compromising and pragmatic.) The Brotherhood has also long emphasized evolutionary politics, as opposed to seizing power in coups d’etat. Some of the Brotherhood’s thinkers have advocated a strategy of gradually converting souls, even if it takes generations, so that Islamic revolution will arrive in the end like a peaceful tide, never to recede.

The Brotherhood draws to an unusual degree on well-educated, talented, dedicated individuals—doctors, lawyers, accountants, and engineers. Where its branches build popular support, as they have done in Egypt and Tunisia, it is often because the Brotherhood’s charitable and social-welfare activity—the hospitals and schools that it runs—is well organized.

Skeptics of the movement have long argued that the Brotherhood is, at its core, anti-democratic (as well as anti-Semitic, about which there can be little doubt). If the Brotherhood occasionally shares power in a particular national democratic setup, this argument goes, it is only as a short-term tactical maneuver, in preparation for dictatorship. Nor, these skeptics continue, will the Egyptian Brotherhood or Hamas ever accept Israel’s legitimacy or national rights.

That view certainly got a lift last Saturday, when Khaled Meshal, Hamas’s political leader, told a mass rally in Gaza that Israel would be wiped out through military force, and that a Palestinian state should be created “from resistance, not negotiation.” Meshal, who stood before a tall rocket erected to represent Hamas’s military prowess, went on:

We will never recognize the legitimacy of the Israeli occupation, and therefore there is no legitimacy for Israel, no matter how long it will take. We will free Jerusalem inch by inch, stone by stone.

Those who favor engagement with Hamas and the Egyptian Brotherhood dismiss such rhetoric as nothing new; they contend that it should be understood as base-rallying political speech, akin to the provocative territorial and demographic claims issued regularly by Israel’s right-wing politicians, and that Hamas and the Brotherhood contain many pragmatists and peaceful politicians. The Egyptian Brotherhood once had an armed wing, but gave it up under international pressure. Hamas has entered into truces with Israel and could conceivably accept a long, stabilizing peace without necessarily dropping its rhetoric.

A problem with these sorts of arguments is that they can succumb to an either-or fallacy. In fact, the Brotherhood is at once a revolutionary, antidemocratic movement and an adaptable force that can be co-opted at times into peaceful democratic politics. In that respect, it resembles international Communism during the Cold War: that ideological movement produced both Italy’s elected, technocratic Communist mayors and the Soviet Union’s Stalinist gulags.

Never before, however, has the Egyptian Brotherhood faced such stark choices about accommodating democratic opponents. In part, that is because the Brotherhood has never been so close to holding national power. Turkey’s Justice and Development Party has shown that an Islamist opposition movement can adapt to governing in a pluralistic system (even if the party’s authoritarian tendencies taint the government’s performance, as has happened in Turkey). But many Brotherhood branches have failed to make the transition from fevered opposition to power sharing and governing when given the opportunity. The direction that Mohamed Morsi steers in during the weeks ahead may define the limits—or the potential—of Islamist politics in the Arab world for many years to come.

Photograph, of Mohamed Morsi, by Daniel Berehulak/Getty.