For a stark example of the shifting politics of stem cell research, look no further than President Bush.
When Bush used the first veto of his presidency to send back a stem cell bill less than a year ago, he did so proudly, surrounding himself with "snowflake babies" born from the same kind of frozen embryos that supporters of the bill wanted to make available to researchers.
But when the President vetoed a nearly identical bill Wednesday, he simultaneously issued a new executive order directing his administration to explore new options in stem cell research -- a clear signal that even the staunch opponents of embryonic stem cell research realize the potent politics of an issue that cuts across party lines.
"The American people see stem cell research as a cure to illnesses that plague their family and family members," said Rep. Rahm Emanuel, D-Ill., citing polls that show nearly three-quarters of the public support embryonic stem cell research. "The American people will not be fooled."
The political shift is visible in the potential candidacy of New York City Mayor Michael Bloomberg, a supporter of expanded research who announced his break from the Republican party Tuesday. His possible run is being supported by California Gov. Arnold Schwarzenegger, another champion of additional stem cell research who has led a major initiative to promote such research in his home state.
The Democratic presidential candidates clearly see the issue as a defining distinction between themselves and the GOP field. Speaking Wednesday morning at a gathering of liberal activists in Washington, Sen. Hillary Clinton, D-N.Y., got her loudest applause of the day when she blasted Bush for putting "ideology before science."
"Let me be clear: When I am president, I will lift the ban on stem cell research," Clinton said.
The issue was nowhere near as potent politically back in August 2001, when the president raised eyebrows with his nationally televised announcement that he was instituting a ban on federal funds being used to support embryonic stem cell research.
In what he billed as a compromise, Bush allowed federally funded research to continue on a limited number of stem cell lines upon which experimentation had already begun. But he said he would allow no federal resources to support experimentation on other stem cell lines, since such research requires the destruction of embryos.
Since then, with stem cell research touted as a potential cure for dozens of diseases and afflictions, momentum started building to reverse that ban. Faced with a rebellion in their ranks, Republican leaders allowed a stem cell bill to come to the House and Senate floor in the last Congress -- producing the bill that Bush vetoed with such fanfare last July.
Democrats won control of Congress on a vow to allow federal dollars to support embryonic stem cell research, and they made good on their promise by delivering the bill Bush is vetoing Wednesday. But that is nowhere near the end of the political story.
While many Republicans are joining Democrats in supporting expanded research, lawmakers are just short of the numbers they'd need to overturn a presidential veto. But the emerging 2008 presidential race could push things along.
The entire Democratic presidential field supports changing the president's policy -- something that can be done automatically via an executive order in the next presidential administration.
While many prominent social conservatives are adamantly opposed to any research that involves the destruction of human embryos, two of the leading Republican candidates for president -- Sen. John McCain, R-Ariz., and former New York Mayor Rudolph Giuliani -- have come out in support of reversing the president's ban on new embryonic stem cell research.
McCain holds that position even though he is perhaps the strongest opponent of abortion rights among the leading Republican candidates for president.
"This is a tough issue for those of us in the pro-life community," McCain said last month at a Republican debate at the Ronald Reagan Presidential Library. "I would remind you that these stem cells are either going to be discarded or perpetually frozen."
Another major candidate, former Massachusetts Gov. Mitt Romney once supported a version of the bill being vetoed Wednesday, but now opposes it. He believes that embryonic stem cell research should be legal -- though not supported by federal funds -- and is a strong supporter of the sort of alternate research methods the president is endorsing.
"I have a deep concern about curing disease," Romney said at the debate, with Schwarzenegger and fellow stem cell supporter Nancy Reagan sitting in the front row.
The latest ABC News/Washington Post poll found that 68 percent of the American people back stem cell research. While there's a definite political split -- more than three-quarters of liberals and moderates back the research, compared with 47 percent of conservatives -- the issue has moved far enough into the mainstream that all candidates must confront it.
"Stem cell research has overwhelming support with the American public," said Karlyn Bowman, a senior fellow at the American Enterprise Institute in Washington. "So candidates need to be able to talk about this issue."
ABC's Teddy Davis contributed to this report.