Herman Cain’s chief of staff  today challenged skeptics to explain his candidate’s rising popularity despite the spate of negative campaign reviews.

“If we’re running such a horrible campaign,” Mark Block asked at a panel discussion in downtown Washington, D.C., “why do we keep moving up in the polls?”

Block’s question came as a response to a tense exchange with Sen. Rick Santorum’s senior advisor, John Brabender, who criticized Herman Cain for flip-flopping on abortion and  apparently changing his story regarding the sexual harassment allegations against him. “If you want to be the front-runner,” Brabender said, “I would say make sure you help our Republicans by making sure the candidate is forthcoming.” The exchange was the most pointed event of the morning.

The panel, a 2012 election preview hosted by the National Journal, featured the top advisers to the 2012 Republican Presidential candidates and was moderated by National Journal political correspondent Beth Reinhard and ABC News political director Amy Walter. The eight senior campaign advisers addressed a plethora of topics on the panel, including their early state strategies, negative ads and the role that outside groups will play in the coming cycle.

Block stayed on-message despite the controversies surrounding his candidate. He said that the Cain campaign had one of their best fundraising days on record Monday. The campaign, he said, took in roughly $250,000 in online donations. “That says to me that the American people are sick and tired of politics as usual,” he said.

Block did not answer questions about the sexual harassment allegations. He also refused to comment on the recent story in the Milwaukee Journal Sentinel in which Cain is accused of allowing a tax-exempt charity to provide money illegally to help get his campaign get up and running, except to say that the campaign has “maintained independent, outside counsel to take a look at the Sentinel story and report back to us.”