When he took office last year, President Obama told his foreign policy advisers that he had two baskets of issues to deal with. The first would be the legacy issues left from his predecessor, like Iraq, Afghanistan and America's image in the world. The second would be his own agenda for the future.

After 15 months addressing the vexing matters he inherited, Mr. Obama is now aggressively advancing his own vision of foreign policy and defining himself more clearly on the world stage. The 47-nation conference on nuclear security he wrapped up on Tuesday represented a chance to assert proactive leadership rather than simply showing that he is not George W. Bush.

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