HONG KONG — It is the best of times because leaders from developed and developing countries have gathered in one place, Washington, to try to rebuild a broken global system, and China and India are at last at the top table.

It is the worst of times because it is an act of supreme vainglory by a lame-duck U.S. president to imagine that in two days (Friday and Saturday) he can fix a shattered system with the help of such an odd assortment of leaders who all have their own agendas.

The best would be for the leaders to agree on ameliorative measures to halt the global economy's progress from recession to depression and — maybe — to set out the ambitions and a time frame for a new conference to destroy the poisonous spider's web of problems threatening the global economy.