JMG has the quote:

"Mitt Romney’s attack on the moral character of disabled veterans, elderly and disabled Social Security recipients, and hard-working Americans in low-wage jobs because they do not pay income taxes is especially galling given the great energy he has put into evading income taxes on his very high income. Many of those whom Mr. Romney impugns pay a significant portion of their income in payroll taxes which support Social Security and Medicare. And until Mr. Romney stops hiding his own tax records, we can speculate that those people pay a higher percentage of their income in these taxes than Mr. Romney does on his foreign accounts, tax shelters, and other evasive devices."