Republican presidential candidate Mitt Romney fought back on Friday against Democrats' claims that he paid no taxes in some years, releasing a letter from his accountants saying he paid. What he did pay was an effective federal tax rate of at least 13.6 percent annually over 20 years. Despite heavy political pressure, Romney stood firm in refusing to make those returns public. It showed he paid $1.9 million in taxes on more than $13 million in income - an effective tax rate of 14.1 percent. That is a lower rate than most American wage-earners pay.