President Obama’s campaign is developing an aggressive new program to expand support from ethnic minority groups and other traditional Democratic voters as his team studies an increasingly narrow path to victory in next year’s reelection effort. The program, called “Operation Vote,” underscores how the tide has turned for Obama, whose 2008 brand was built on calls to unite “red and blue America.” Then, he presented himself as a politician who could transcend traditional partisan divisions, and many white centrists were drawn to the coalition that helped elect the country’s first black president. Today, the political realities of a sputtering economy,...