In response, the chairman of the Republican National Committee, Reince Priebus, on Sunday's Fox News, called Sen. Reid a "dirty liar" (video below).
In an interview with Politico.com, Reid's chief of staff David Krone responded by calling Republicans "a bunch of cowards" and "henchmen for Romney."
"To turn it around, all their childish rants this weekend about calling Reid a 'liar' and all that, it just shows you how scared they are that Harry Reid was telling the truth."
Sen. Reid's spokesman Adam Jentleson backed up the credibility of Sen. Reid's anonymous Bain Capital source and dared Romney to debunk Sen. Reid's claim by releasing more tax returns.
Jentleson told TalkingPointsMemo.com: "It's clear Mitt Romney is hiding something, and the only way for him to clear this up is to be straight with the American people and release his tax returns.
If Romney's tax returns were clean and defensible they would have been produced long ago. If there are just some problems or embarrassments in them they would be declared now so as to get it all out of the way. Leaving the returns outstanding as the campaign drags on speaks volumes. The GOP is in a bad box. They can't doctor the actual returns.
Turn up the heat! Make 'em squirm. Romney is a Tax Dodger! Romney the weasel, the cheat! Romney took the amnesty for offshore holdings. The more the GOP are defensively shrill, the more they should be denounced. Pound them relentlessly on every level, through every media. Make this issue a defining one.