Given Mugabe's history, this smacks of naivete. But Tsvangirai believes he has a realistic political approach. "You don't expect people who were violent yesterday to wake up one morning and become peaceful." So his strategy is to "build institutions in the course of time" -- particularly through the process of writing a new constitution, leading to new elections. Tsvangirai talks again and again of "institutions" and "mechanisms" and "political architecture" as the methods to make democracy irreversible. His intention is to fight arbitrary and personal rule with the weapons of process -- a Madisonian response to a Neronian dictator.

Four months into the unity government, the results are mixed. The prime minister deserves credit for beginning to stabilize the economy, particularly controlling Zimbabwe's legendary inflation. In August 2008, Zimbabwe's central bank revalued its currency by removing 10 zeroes from its currency; five months later, it removed 12 more. Now the country has essentially scrapped its currency and moved to an economy based on the American dollar and the South African rand. While 70 percent of the population still depends on food aid, goods are back in the stores.

But Mugabe's ruling party remains in charge of the secret police and key ministries. It continues to harass opponents and confiscate farmland. Tsvangirai optimistically calls these elements a "dwindling remnant" -- but it hard to imagine that they will dwindle without a fight. And Mugabe has asserted his dominance with the appointment of political cronies in blatant violation of the power-sharing agreement -- so far with little consequence.

It was this point that Tsvangirai emphasized during his recent U.S. visit, calling on Mugabe's brutal attorney general and corrupt reserve bank governor to step down -- and the world to insist upon these outcomes. This represents a test for South Africa's new president, Jacob Zuma: Will he abandon the "quiet diplomacy" of his predecessor, which often amounted to permission for Mugabe's abuses, and insist that the power-sharing agreement be enforced? It is a test for President Obama: Will he pressure Zuma to do the right thing? And it is a test for the power- sharing agreement itself. A stalemate on these appointments, Tsvangirai admits, would "undermine the credibility of the new dispensation."

Tsvangirai's strategy -- using a power-sharing arrangement with a tyrant to gradually end a tyrant's power -- has little precedent of success. If Tsvangirai fails, he will be just another victim of Mugabe's charming ruthlessness. But if the prime minister succeeds, he will be an exceptional statesman, who set aside his own claims of justice for the peace and progress of his country. And he would become Zimbabwe's true founder.