Senate passage of legislation to expand embryonic stem cell research leaves supporters facing the difficult task of persuading a Republican to switch sides in order to hand Democrats a purely political victory.

The bill (S 5), which passed Wednesday, 63-34, would overturn President Bush’s ban on federal research funding for new embryonic stem cell lines. A competing bill (S 30) to promote alternative methods of stem cell research also passed, 70-28.

Bush has vowed to veto the legislation that would lift his ban, which has been in place since Aug. 9, 2001.

With 66 votes in favor of a veto override — three bill supporters were absent from Wednesday’s vote — advocates need at least one opposing senator to switch sides to reach the 67-vote threshold for an override. Since neither of the two Democrats who voted against the measure is likely to switch his vote, supporters will have to target a Republican.

A two-thirds majority for an override appears out of reach in the House, which passed its stem cell bill (HR 3) on Jan. 11 by a vote of 253-174. So a Senate override would amount to a political victory for Democrats and a rebuke to Bush.

The issue has strong public support, but it will be especially difficult to persuade a Republican senator to flip when the bill likely will never become law with Bush in the White House.

Sen. Tom Harkin, D-Iowa, however, has expressed optimism that a senator may exercise the political contortion he seeks. “As I said, I remain a hopeful man,” he said. “I hope the president signs it. If he doesn’t, I hope we have the one more vote we need to override the veto. People do change their minds.”

Standing next to him just after the bill’s passage, Arlen Specter, R-Pa., gave a more forceful outlook in finding an extra Senate vote, and even securing a House override.

“Votes are changed in the face of political pressure from constituents and voters,” Specter said. “With enough public pressure, we could override a veto this year.”

Bob Casey, D-Pa.; Norm Coleman, R-Minn., the competing bill’s sponsor; and John E. Sununu, R-N.H., were initial targets for swing votes. All voted against passage of the embryonic stem cell research bill. Coleman and Casey said they do not support an override. Ben Nelson of Nebraska, the other Democrat who voted “no” Wednesday, is also unlikely to switch.

Sununu could not be reached for comment.

Bush and other social conservatives liken embryonic stem cell research to abortion because embryos are destroyed. Supporters of the research see it as holding the potential for treatment of diseases such as diabetes, Alzheimer’s and Parkinson’s.

Coleman’s bill (S 30) was viewed by the other measure’s supporters as a way to provide political cover for senators who want to support research that could lead to medical advances but who are morally opposed to the extraction of cells from embryos.

Coleman, who is up for re-election next year, disputed that characterization.

“It’s not political cover,” he said. “The reality is, there aren’t enough votes in the House to override a veto.”

His bill is cosponsored by a half-dozen other Republicans, including Minority Leader Mitch McConnell of Kentucky. It would promote research on stem cells that does not involve “the destruction or discarding of, or risk of injury to, a human embryo or embryos other than those that are naturally dead.”

Coleman said he offered it as a way of getting new federal support for stem cell research, without crossing moral boundaries. “The question becomes, how do we move forward, not just in the debate but action,” he said.

Coleman said he did not know whether the House would take up his bill.

The House is expected to clear the Senate’s embryonic stem cell measure after it returns next week from its spring recess. Language that would promote research on stem cells not derived from embryos is not in the House version.

Because the bill sent to Bush will have originated in the Senate, that chamber would vote first on a veto override.

As senators debated the bill April 10 and Wednesday, they frequently invoked the March 19 Senate testimony of Dr. Elias Zerhouni, director of the National Institutes of Health (NIH). Zerhouni, a Bush appointee, broke with administration policy and told lawmakers that science and the nation would be better served by reversing Bush’s 2001 order.

On Wednesday, the NIH declined to comment further on Zerhouni’s testimony or whether it might affect his future there.

First posted April 11, 2007 1:38 p.m.