That's because embryonic stem cells come from frozen embryos, the result of in vitro fertilizations, and not everyone agrees on what should be done with them when couples don't want them.
Should these frozen embryos be thrown away? Adopted? Or given to science?
On Friday, in a break with Mr. Bush, Senate Majority Leader Bill.
The battle is one in which Cody Unser has a critical, personal interest and an active part.
The teenage daughter of retired star racecar driver Al Unser Jr., a two-time Indianapolis 500 winner, was in sixth grade when she collapsed at school. Doctors at the hospital thought it was the flu and sent her home.
It turned out to be much more than that, reports Hattie Kauffman on The Early Show Monday in the first of a two-part series, "Two Faces of Hope."
"In 20 minutes, my legs were paralyzed. I had no idea what was going on," Cody says.
Now 18, Cody was 12 years old, playing basketball, when a blinding headache left her breathless.
"When I woke up the next morning, my legs couldn't move. And I couldn't go to the bathroom. And so it just kind of snowballed from there," she recalls.
Cody was diagnosed with a rare neurological disorder, transverse myelitis. Her own immune system attacked her spinal cord. She would likely never walk again.
"It should be me that's there, and it's just not fair to grab a little girl like this who's got her whole life in front of her," Al Unser. Jr. told 48 Hours in September 2000.
"When we were initially in it, I just thought … how does a mother, how does her family get through something like this?" says Cody's mom, Shelley Unser.
But, observes Kauffman, Cody refused to be defeated.
At 13, she started her own foundation, the Cody Unser First Step Foundation, and today, Cody fights hard for a cure, via embryonic stem cells.
"I think," she tells Kauffman, "stem cell research could help me by, you know, maybe one day making me walk, making me be able to put my feet on the sand and be able to feel, you know, what sand feels like again."
"Cody has had such an injury to her spinal cord that the only way we are going to rewire that spinal cord and to get her to walk is through the use of stem cells, and even specifically, embryonic stem cells," says embryonic stem cell researcher Dr. Douglas Kerr of Johns Hopkins University, who is Cody's physician.
Pointing to an image of magnified cells, he says, "This is simply a cluster of cells. There are no tissues. There's no organs. There's no beating heart."
Foes of stem cell research argue it uses cells that could become human beings.
Embryonic stem cells are valuable, Kauffman explains, because they hold the blueprint for every cell in the body. The hope for Cody is to direct these cells to become the neurons missing in her spine.
But Kerr's research has been stymied by federal restrictions.
"It's very frustrating to see this," he laments, "because, as a physician, I grieve with these patients."
Cody has spoken before Congress, urging it to lift curbs on embryonic stem cell research, saying, "Even though I may be paralyzed, my voice is not."
And she's met the president.
Gazing at a photo of Cody and Mr. Bush, Shelley said, "I look at this picture of her and the president, and I wonder what would he do if it was his daughter."
"That was really tough for me," Cody says. "He inspired everyone to, you know, continue with this. …There's no way that we're gonna let him down."
She wears a Superman pendant, and writes positive messages all over her walls, such as, "You have to stand up for something, or fall for anything."
When Cody became paralyzed six years ago, she set one goal that has remained unfulfilled.
"That was my first, initial dream was to be able to walk, dancing at my senior prom."
"It's weird moments, like the prom," cried Shelley.
Through her tears, Shelley continued, "She had a blast. They looked great. She'll make the best of anything. But, I cry because I know that it hurts her, and she doesn't let anybody know."
"Sometimes, I do get depressed," Cody says in response to a Kauffman query, "but it's my friends and my family that really pull me out of it."
To those who say it would be morally wrong to conduct stem cell research, Cody has an answer.
"I've heard a lot of morals and ethics with this whole issue. And my thing is that, it would be morally wrong to deny hope. It'd be morally wrong to say, 'No, you have to be like this for the rest of your life.' "
As the debate plays out, Cody is confident she'll someday leave her wheels behind, and walk again: "There's just so much out there right now that, you know, the world has so much to offer, and I can't wait to go out and grab it and get to experience everything and live life to the fullest."
Mr. Bush has said he would veto any bill overturning his restrictions on stem cell research, Kauffman says.
According to Kerr, human clinical trials for stem cell-based treatments of some paralysis are three to five years away.
But, says Kauffman, Kerr adds that doctors could have begun clinical trials by now if there had never been restrictions on federal funding of stem cell research.
In the second part of "Two Faces of Hope" on Tuesday, The Early Show will introduce viewers to a couple who opposes stem cell research and chose instead to donate their embryo to another couple who wanted a baby.>