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Standing with millionaires and their assistants, President Barack Obama makes a statement about the "Buffett rule" in the Eisenhower Executive Office Building on April 11 in Washington, D.C.

Named after the billionare investor Warren Buffett, the Buffett rule would ensure that the wealthiest Americans pay at least 30 percent of their income in federal taxes. The proposal is a centerpiece of Obama's re-election campaign.