Iran is about to hold a national election that could shape the country's future for a generation — potentially even more so than the presidential elections in 2009, when "green movement" protests signaled public outrage with the regime, and in 2013, when voters elevated the moderate Hassan Rouhani on a promise of economic and diplomatic opening.

On February 26, Iranians will vote for candidates for their parliament and for a body called the Assembly of Experts — which, though few outside Iran have heard of it, could be in a position to radically alter Iran's politics:

Even Supreme Leader Ali Khamenei, who is 76 years old, has acknowledged the stakes here, hinting that he may well die during the Assembly of Experts' next eight-year term.

"As before, we insist everyone, even those who don't believe in the system and the leadership, come to the ballots, as the election belongs to the nation, and the system," Khamenei said in a speech in Tehran. "That day, when the current leader is not in this world, this committee should choose a leader who holds the key to the movement of this revolution."

Iranian politics are currently divided between moderates and hard-liners, but 2013 marked the ascendance of moderates, who have in turn showed their political power by securing the nuclear deal and a reduction in sanctions. There's reason to believe that moderates could be poised to do well in the upcoming elections as a result.

There is thus a real chance that moderates could end up dominating the next Assembly of Experts, who will likely be in office when Khamenei dies or retires. The process by which they would vet and select a new leader has its own complex politics, but a more moderate Assembly of Experts could in turn select a more moderate supreme leader to replace Khamenei — changing the course of Iran's future for a generation or more.

This all speaks to one of the most common misconceptions about Iran: that it has no politics to speak of. It's an understandable thing to think: The country's paramount leader is an unelected, lifelong figure literally called the "supreme leader," after all. That doesn't sound like a place where politics and elections would make much of a difference.

Iranian politics are indeed constrained by authoritarianism. Opposition candidates are jailed or put under house arrest. Iranians who protested apparently fraudulent election results in 2009 faced violent, deadly crackdowns. Yet at the same time, Iran does have popularly elected bodies with real power, institutions that push against one another, and political factions that are constantly at one another's throats, jockeying for power and influence to see through their dramatically clashing visions for the country.

Iran is not a democracy, in other words, but rather an autocracy with democratic elements — a legacy of its 1979 revolution, in which revolutionary leaders with drastically different visions and little governing experience slapped together a convoluted mess of a political system that was somehow meant to be both a democracy and a theocracy. If those two systems sound incompatible, it's because they are, and the tension between them has defined Iran and its politics ever since.

February's Assembly of Experts election will, in many ways, be at the intersection of those two versions of Iran, the democracy and the theocracy. Iranians elect their president every few years, but the president's power is limited by the supreme leader, particularly on the issues that most determine Iran's place in the world: its foreign policy and its military affairs.

The supreme leader is only truly subservient to democracy for one day: the day of his selection. What happens on that day, when Khamenei dies and a successor is picked, will be determined by February's vote, in which both moderates and hard-liners are running.

This February vote, then, is the closest that Iranian popular will and internal politics can come to shaping the country's future — it is, in a sense, more meaningful than even the presidential elections, which, for all their flaws, in both 2009 and 2013 changed the country's course.

Assuming Khamenei dies or resigns before reaching age 84, this is quite literally a once-in-a-lifetime event, and its consequences will last as long as the next supreme leader reigns, which could be decades.