The Nevada Democrat ignited a firestorm late July after he said an informed Bain investor told him that Romney hadn't paid taxes for a decade. Lacking evidence for his claim, Reid faced fierce criticism, but repeatedly stood by his charge, putting the Republican nominee on defense for weeks over his taxes.
Romney has released a partial tax return for 2010 and says he'll release only one more year. He has emphatically denied Reid's claim, and the senator did not repeat it Tuesday night.
Tax fairness is a central plank of the Obama campaign's re-election bid.
"Today's Republican Party believes in two sets of rules -- one for millionaires and billionaires and another for the middle class," Reid said. "And this year they've nominated the strongest proponent and clearest beneficiary of this rigged game: Mitt Romney."