The resignation of Mr. Yukio Hatoyama as president of the Democratic Party of Japan, just two months after his re-election, is probably the most poignant reminder yet that the nation's largest opposition party is deeply divided. On Tuesday, taking the blame for his abortive plan to forge an opposition alliance, Mr. Hatoyama announced he will formally step down on Dec. 13, the last day of the current Diet session.

The Hatoyama fiasco is having a profound impact on the DPJ, which now faces the most critical moment in its history. His resignation was inevitable, given his plummeting leadership, but there is no assurance that the divided party will stand on its feet anytime soon. Mr. Hatoyama's ill-fated plan, which he abruptly floated without first consulting the party, has been criticized by many as "reckless," but blaming him alone cannot solve the party's problems. The disarray in the DPJ will continue unless it puts its house in order.

The DPJ crisis is also likely to have an effect on other opposition parties, for the public's disappointment with the DPJ will lead to an erosion of confidence in the opposition camp as a whole. A weakening of opposition ranks, already evident in the Diet and elsewhere, will further embolden the ruling parties. As a result, politics may lose some of its vital flexibility to the detriment of sound parliamentary democracy in Japan.