Much media speculation has surrounded whether the term has meaning in North Africa. Allen's mother was Franco-Tunisian and spoke French, as reportedly did Allen and his siblings.
At least one expert on Tunisian history who spoke to ABC News says that "macaca" was a derogatory term used by French colonists in Tunisia to describe the indigenous Africans centuries ago, though neither an employee of the Tunisian Embassy to the U.S. nor a former ambassador to Tunisia had ever heard the term "macaca" before.
Allen insisted today that "it's an absolutely meaningless word to me, and for folks to think I would know the genus of monkey are in eastern Asia, ascribe a lot more intelligence to me then I actually have," he said.
Reached at a campaign event in Arlington, VA, Webb said he doesn't buy Allen's explanation though he largely held his fire.
When asked, Webb responded: "George Allen knew what he was saying and he's the one you need to talk to about why he said it."
Republicans argue there's a double-standard -- that the media didn't seem to care when Democratic Senator Joe Biden, also a 2008 hopeful also offended Indian Americans.
"You cannot go to a 7-eleven or a Dunkin' Donuts unless you have a slight Indian accent. I'm not joking," Biden said.
Nor did the media seem to make a big deal, conservatives say, when Webb's campaign -- running against a Jewish candidate in the primary -- used imagery in a flier that some found anti-Semitic.
However, Sabato argues that Allen is a special case. "He has had a whole series of events in his personal and political life that have caused reasonable people to question whether he is sensitive to racial issues," he said.
In May, the liberal New Republic magazine highlighted what it called Allen's "race problem" -- including an affinity for the confederate flag Allen had as far back as his time as a high school student in California. As a Virginia state legislator, Allen led the charge against a Martin Luther King day holiday. And as governor he issued a proclamation honoring the confederacy with nary a mention of slavery.
When asked by ABC News about the "macaca" brouhaha being part of a supposed larger history of racial insensitvity, Allen said, "I don't see how this has anything to do with any of that."
Today, even Allen's conservative supporters have begun to raise questions. Webb is so vastly underfunded he remains a longshot candidate to defeat Allen, but Allen felt the compelling need to run damage control, not necessarily because of 2006 -- but perhaps 2008.
"I don't think there's any chance this will hurt Allen in this re-election race, at least not enough to cost him the election," Sabato said. "But the presidency is another matter entirely. There are very few people left in either party who want to nominate somebody who has a history of racial insensitivity."
And even those who appeared with Allen when he made his mea culpa appeared to send this message.
Allen thanked his Indian American guests for coming -- Shurkiyah," he said, using the Hindi word for "thank you," a moment of multicultural contrition indicating how serious he is about putting this behind him --before running off for a campaign event in Norfolk. But Sanjay Puri, the head of an Indian American political action committee, the only attendee Allen's campaign allowed ABC News to talk to, said he didn't know if he would vote for Allen.
This was far from the end of things, Puri said. "I think that this is the beginning and I believe that was what was clearly told to Senator Allen," he said. "We expect a lot better from our leaders. Definitely a lot better from our leaders."
In Norfolk, Allen appeared with Senator John McCain, R-Ariz., at an event aimed at veterans. The Virginian was no doubt happy for a change of subject. But it's entirely possible that in two years, in the throes of the GOP primaries, it may be McCain questioning just what his colleague meant when he used the word "macaca."
Katie Hinman and Teddy Davis contributed to this report