A question Democrats can't answer

Washington Examiner Editorial:

If top 5% paid 40% of taxes, what is their 'fair' share?

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Although Obama and his fellow Democrats repeatedly call on wealthier Americans to pay their "fair share," they never specify what percentage of the nation's tax burden the wealthy would have to bear. As matters stand, the top 1 percent of American households paid 39 percent of income taxes in 2009, according to the most recent data compiled by the Congressional Budget Office, and the top 5 percent of taxpayers paid 64 percent. 

But income taxes, taken in isolation, do not tell the whole story, because lower-income Americans do pay payroll taxes. But even taking into account all forms of taxation, the top 1 percent still paid 22 percent of federal taxes while earning just 13.4 percent of household income. The top 5 percent paid 40 percent of all federal taxes, despite earning only 26 percent of all income. No matter how you slice the numbers, it's hard to understand why anyone would think the wealthy aren't already shouldering a burden commensurate with their blessings.
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The fact is that these people are already paying more than their fair share of the taxes.  Perhaps the question should be what is the fair share of taxes to be paid by those making less?  What should they contribute for all the services they receive from government?