President Obama's relentless advocacy of the Buffett Rule—legislation to compel Americans earning $1 million or more annually to pay 30% of it in income taxes—moved last Saturday from misleading to incoherent. The occasion was Mr. Obama's weekly radio address, when he explained the tax was "about growth...about being able to make the investments we need to strengthen our economy and create jobs."

This was at least the president's third rationale for the new tax. Last September, Mr. Obama told a California fundraiser that the Buffett Rule was needed to "stabilize our debt and deficits for the next decade."

That argument would fizzle: The tax revenues to be raised over a decade—$46.7 billion, according to the congressional Joint Committee on Taxation—would cover one-half of 1% of Mr. Obama's proposed budget over the same time period.

In January, Mr. Obama made another argument in his State of the Union address. The Buffett Rule, he said, was essential "to change our tax code so that people like me . . . pay our fair share of taxes." But as many pointed out, why is it fair to increase the burden on the roughly 236,000 individual taxpayers—less than two-tenths of 1% of the 145 million filers in 2011—who already paid 21% of all income taxes?

Karl Rove is a Fox News contributor. He is the former senior adviser and deputy chief of staff to President George W. Bush.  To continue reading his column on President Obama and the Buffet rule in the Wall Street Journal, click here. For more visit Rove.com.