A television ad in the New Jersey governor's race that appeared last week for Senator Jon S. Corzine features a young man named Carl Riccio who tells viewers, from his wheelchair, that embryonic stem cell research "is the most hopeful thing for spinal cord injuries." He goes on to say that Douglas R. Forrester "doesn't support embryonic stem cell research, therefore I don't think he supports people like me and doctors who say a cure is coming."

The style is simple. There is no foreboding narrator, no eye-catching graphics. But the topic and the understated, yet stinging, approach seem to have hammered a nerve. Tom Shea, one of Senator Corzine's advisers, said the ad had been downloaded more than 5,000 times from the campaign's Web site since last Tuesday, making it the campaign's most popular online video by a factor of 10.

Mr. Forrester, meanwhile, spent much of last week trying to blunt the commercial's impact, even as the public at large debated the harm and rewards that come with its unification of cause, patient and candidate.

"This ad goes to the edge and comes close to going beyond," said David P. Rebovich, a political science professor at Rider University. "The young man seems to say if you don't vote for Jon Corzine, I'm stuck in this wheelchair forever."

The argument over stem cell research, of course, is nothing new. Since the last presidential election there has been a vigorous debate over the ethics of using stem cells gathered from human embryos, which must be destroyed in the process.

When Democrats in 2004 relied on posthumous television appeals from Christopher Reeve, conservatives and bioethicists questioned what the public would glean from them. Would people think that breakthroughs were just around the corner when many scientists believe that treatments are actually at least a decade away? Were patients and their hope for a cure being exploited to benefit the careers of politicians and scientists?

The Riccio ad has brought back many of these questions. John M. Haas, president of the National Catholic Bioethics Center, in Philadelphia, and other opponents of embryonic stem cell research denounced the ad as inaccurate and inhumane. Advocates for the disabled praised the ad for what they said was its blunt honesty.

This time, though, the thrust of the argument has been seasoned with a touch of rancor.

"The difference here is that the Corzine people have made it not about simply stem cell research," said Trevor Parry-Giles, a professor of political culture at the University of Maryland. "They've made it about the negative politics of the governor's race. The risk here is that instead of coming off as a champion of stem cell research, he comes off as political hack, using someone in a vulnerable position for what seems like illegitimate political gain. That's exactly the wrong message you want to send."

Mr. Shea, Senator Corzine's adviser, said that the ad was simply a testimonial. "It was completely unscripted," he said Thursday, adding that no viewers had sent e-mail messages to complain about its content. "The ad is Carl Riccio in his own words."

Mr. Riccio, 19, in a telephone interview from Villanova University, where he is a sophomore, concurred. "They asked me what I knew about Forrester and why I did not support Forrester over Corzine," he said. And some medical experts found Mr. Riccio's comments well within the boundaries of the stem cell debate.

"It's absolutely the same as what's gone on in Massachusetts and California," said Arthur L. Caplan, chairman of the Department of Medical Ethics at the University of Pennsylvania. "It's a tough stance, but it doesn't strike me as out of bounds."

Regardless of the ad's ethics, however, there was no denying its power to affect the campaign.

Last Tuesday, Sherry Sylvester, Mr. Forrester's spokeswoman, issued a statement that said Mr. Forrester supports stem cell research, and in an interview she confirmed that his support extended to embryonic stem cells. This reflected something of a reversal from his earlier opposition to embryonic stem cells (which had him in line with the Bush administration) and came about a week after he said that his position had "evolved."

The campaign was also careful not to be overly critical of Mr. Riccio, who was paralyzed in a high school wrestling accident, or the ad's scientific premise.

The campaign of Mr. Forrester, whose daughter Briana, 19, is recuperating from a brain hemorrhage, released a statement to show his connection to people who might benefit from the research.

"Doug, because he has a daughter with a brain injury, is particularly attuned to these challenges," Ms. Sylvester said. "Doug was only sorry that the young man didn't understand his position."

Patients who could benefit from stem cells, it seems, have become the latest highly valued endorsement worth trotting out. Polls show that a majority of Americans support embryonic stem cell research and while Democrats have had more success with the issue, that might be changing. Prominent Republicans like Bill Frist, the Senate majority leader; Nancy Reagan; and now Doug Forrester all seem to have fallen under the sway of patient advocates.