President Obama has elevated one question to a key campaign issue — what is a “fair share” of taxes?

Obama repeatedly invokes tax fairness as a major campaign issue, returning over and over to the phrase “fair share,” as he did on June 22 when he talked about a policy “that asks the wealthiest Americans to help pay down our deficit, to do their fair share.”

At a May 14 campaign stop, he used similar language, saying the idea is to make “sure that everybody is paying their fair share.”

Republicans, however, question the premise.

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