President Bush warned Monday he would veto any attempt by Congress to expand federally funded embryonic stem-cell research beyond the plan he unveiled last week.
"The statement I laid out is what I think is right for America. And any piece of legislation that undermines what I think is right will be vetoed," Mr. Bush told reporters in Crawford, Texas, where he is vacationing.
Mr. Bush last week approved spending taxpayer dollars for stem-cell research limited to about 60 stem-cell lines believed in existence from embryos that were destroyed in the process.
Senate Majority Leader Tom Daschle, D-S.D., predicted last week that "the Senate will want to take action" to open up more research funding but didn't say whether he would support it.
Many abortion opponents, including Roman Catholic leaders, think Mr. Bush's decision goes too far.
Joseph A. Fiorenza, president of the National Conference of Catholic Bishops, said on ABC that he considered the existing stem cell lines "ill-gotten goods."
"For the government to allow funding for this experiment makes the government complicit in what we consider to be wrongdoing," Fiorenza said.
Speaking on NBC, Health and Human Services Secretary Tommy Thompson, who is Catholic, said the president's decision is moral because it will only allow federal funding of research on embryos that have already been destroyed.
"Are we just going to throw them in the garbage can and say there's nothing that can be done on them? You can't put them back together," Thompson said. "Allow the research to continue."
In an effort to further explain the reasoning behind his stem cell decision, the president took to the Op-Ed page of the New York Times.
In a piece under his byline, Mr. Bush wrote that, while it is unethical to end life in medical research, it is ethical to benefit from research where life and death decisions have already been made.
It's a justification of his decision to fund research on existing embryonic stem cells - but not on those that would require the destruction of additional embryos. He wrote that for him it's "a matter of conviction."
Thompson estimated stem cell researchers were three to five years from any breakthroughs in the search for cures for Alzheimer's disease, juvenile diabetes and other diseases.
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