President Bush hasn't seen the last of legislation to allow federal funding for new embryonic stem cell research.

Supporters are answering his veto with an effort Thursday to add to an appropriations bill permission to use taxpayer dollars for new lines of embryonic stem cells.

Separately, Democratic congressional leaders are expected to bring back the bill Bush nixed and try to override his veto — or just give the issue more air time. Neither chamber has the two-thirds majority necessary to succeed.

In the longer term, the stem cell issue will dog any candidate who sides with Bush, supporters of the legislation say.

"This will be an election issue in 2008 not just in the House, not just in the Senate, but in the presidential election," said one of the House's chief sponsors of the bill Bush vetoed, Rep. Diana DeGette, D-Colo. "We ... intend to continue bringing this up until we have a pro-stem cell president and a pro-stem cell Congress."

It was familiar rhetoric after Bush's second veto of the legislation. But this time, he is facing new Democratic congressional leaders planning to resurrect the issue in the bills they author, the committees they control and on the House and Senate floors.

Vetoing the bill a second time Wednesday, Bush also sought to placate those who disagree with him by signing an executive order urging scientists toward what he termed "ethically responsible" research.

Bush announced no new federal dollars for stem cell research, which supporters say holds the promise of disease cures, and his order would not allow researchers to do anything they couldn't do under existing restrictions.

"If this legislation became law, it would compel American taxpayers for the first time in our history to support the deliberate destruction of human embryos," Bush said. "I made it clear to Congress and to the American people that I will not allow our nation to cross this moral line."

He vetoed similar embryonic stem cell legislation last July.

Bush's executive order encourages scientists to work with the government to add other kinds of stem cell research to the list of projects eligible for federal funding — so long as it does not create, harm or destroy human embryos.

Democrats dismissed Bush's veto as a moral affront to hundreds of thousands of Americans who have diseases that might someday be treated or cured by research into the lines derived from pluripotent - or all-purpose - embryonic stem cells. Democrats said his executive order was a meaningless gesture meant to trick people into thinking he had advanced stem cell research.

Many Republicans also support the bill Bush vetoed. At a separate news conference, DeGette's co-sponsor, Rep. Mike Castle, R-Del., said Republican supporters will join in the effort to overturn the veto.

The pushback was expected to begin Thursday. The Senate Appropriations Committee was to vote on a must-pass bill for the Labor and Health and Human Services departments that includes permission to use federal funding for embryonic stem cell lines derived after Bush in 2001 banned taxpayer dollars from being used on new studies of that kind.

The provision, proposed by Sen. Tom Harkin, D-Iowa, would allow taxpayer dollars to be spent on research on human embryonic stem cell lines derived prior to June 15, 2007 — moving the date of Bush's August 2001 ban on public funding for such research up by nearly six years.

Research on stem cell lines derived in the interim would be eligible for federal funding. The new provision also would add ethical standards to be used for selecting embryos to be studied using federal funds.

By the 2008 elections, Democrats predicted, Bush's veto of new public funding for embryonic stem cell research would be a top priority of voters in the congressional and presidential elections.

Public opinion polls show strong support for the research.

Republican presidential hopefuls are split on the scope of federal involvement in embryonic stem cell research. Sen. John McCain of Arizona and former New York Mayor Rudy Giuliani have broken with Bush — and the GOP's social conservatives — in backing the expansion of federal funding for such research.

Rivals Mitt Romney and Sen. Sam Brownback of Kansas oppose the expansion.

Most of the Democratic candidates have urged Bush to expand the research.

Scientists were first able to conduct research with embryonic stem cells in 1998, according to the National Institutes of Health. There were no federal funds available for the work until Bush announced on Aug. 9, 2001, that his administration would spend tax money for research on lines of cells that already were in existence.

Currently, states and private organizations are permitted to fund embryonic stem cell research, but federal support is limited to cells that existed as of Aug. 9, 2001. The latest bill was aimed at lifting that restriction.

The bill is S. 5.