WHEN JAPAN suffered its terrible earthquake in March, there was hope for a silver lining: Perhaps the squabbling, ineffectual leadership class in Tokyo would pull together and rally to the cause of reconstruction.

So far, no such luck. Ordinary people affected by the quake won the world’s admiration with their mixture of neighborliness and quiet determination. Japan’s leaders, by contrast, seemed confused, often absent, at times ill-informed and at times misinforming.

It hasn’t gotten better with time. The government is no closer to consensus on the big fiscal questions that divide it — essentially, to tax or not to tax as $200 billion in reconstruction costs are added to the nation’s already gigantic debt. Instead, the earthquake has given rise to a kind of anti-nuclear populism, with leaders promising to reduce Japan’s reliance on the atom without providing any road map for doing so.

On Friday the populist-in-chief on that score, Prime Minister Naoto Kan, resigned — becoming the sixth Japanese leader to step down in five years. Tokyo, like Washington, has divided rule — the upper house of the Diet, or parliament, is controlled by one party, the lower house by another. So picture Washington-style gridlock with the added feature of a new president every year. You can imagine how much gets done.

This matters, and not just to Japan. As a rising China challenges democracies throughout East and Southeast Asia, Japan, with the world’s third-largest economy after the United States and China, should be helping to provide balance. But political instability means Japan is punching below its weight.

Obama administration officials, privately exasperated, continue to emphasize publicly the importance of the alliance, as they should. U.S. assistance during the earthquake, especially from the armed forces, reminded many Japanese of the value of U.S. friendship. Japan houses and helps support U.S. bases that are key to Asian stability. In Afghanistan and elsewhere, Japan continues to offer substantial help.

But only Japan can answer whether the merry-go-round of prime ministers is a transition to a more capable system or a symptom of continuing decline. Mr. Kan’s Democratic Party of Japan in 2009 unseated a party that had ruled pretty much uninterrupted for a half-century, so rookie mistakes should not surprise. Japan could be driving over inevitable bumps on the road to a competitive two-party or multi-party democracy, reshaping the bureaucratic state that had presided, most recently, over two decades of stagnation. The party will choose a new leader Monday, and a number of experienced candidates have emerged, including former foreign minister Seiji Maehara, who helped keep the U.S.-Japan relationship on an even keel during the DPJ’s rocky first year in 2009-10.

On the other hand, Japan is facing an extreme version of the aging-population challenge that is in the cards for America, China and most developed nations, meaning fewer and fewer active workers supporting more and more pensioners. Can an economy and a democracy remain dynamic under that demographic pressure? The early returns from Tokyo aren’t encouraging.