Lungren argued that the issue of stem cell research is complex, and that it was unfair of the ad to boil it down so crudely. The ad was produced by the House Majority PAC, which was working to return House control to Democrats.

"There can be a legitimate debate about the moral and ethical concerns surrounding stem cell research and embryonic stem cell research," he said. "But to have an ad that reduces it to the question of whether a five year can look in the camera and say, why does this congressman want me to die, how does that elevate the debate?

"How does that in any way enhance our ability to make very difficult decisions? Does that condemn anybody who happens to have traditional values consistent with traditional teachings of the Catholic church and other churches? To be ridiculed? To be condemned for a lack of concern for fellow human beings?"

In 2007, Lungren supported an Executive Order from President George W. Bush that supported stem cell research involving cells taken in a way that does not harm living embryos.

Lungren has also sponsored legislation that would make political parties more responsible for the content of the ads they run in support of their candidates. On the floor Tuesday night, Lungren noted that the ad from Bera was run near the end of the campaign.

"And to have the ad run in the last weeks of the campaign without any ability to respond to it," he added. "I ask you, is that civil?

"We hear many in the press decry the level of debate, and yet, not a peep about ads such as that."

— This story was updated at 8:16 a.m., Wednesday, to clarify that the ad was produced by the House Majority PAC.