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 Relief Act of 2010 retroactively reinstate the estate tax for decedents dying in 2010 late in the year after it originally had been scheduled to be repealed for 2010.)