Congress has the power to tax income from whatever source derived. Do you believe that this allows Congress the discretion to tax municipal bond interest (or other tax-exempt income) earned throughout a tax year retroactively if the law to make this income taxable is not enacted until the very end of the tax year? (Note: The Tax Relief Act of 2010 retroactively reinstated the estate tax for decedents dying in 2010 late in the year after it originally had been repealed for 2010.)