Never has postwar Japan needed strong, assertive leadership more — and never has its weak, rudderless system of governing been so clearly exposed. With earthquake, tsunami and nuclear crisis striking in rapid, bewildering succession, Japan’s leaders need skills they are not trained to have: rallying the public, improvising solutions and cooperating with powerful bureaucracies. “Japan has never experienced such a serious test,” said Takeshi Sasaki, a political scientist at Gakushuin University. “At the same time, there is a leadership vacuum.”