With Sen. John McCain poised to announce his vice presidential selection Friday at noon in Ohio, a revolt is brewing among anti-abortion activists in his conservative base that could include a walkout at the Republican National Convention next week and a huge battle on the floor -- especially if he selects former-Democrat-turned-Independent Joe Lieberman.
McCain campaign sources tell ABCNews that the presumptive Republican nominee will announce his pick for vice president at a scheduled event in Dayton, Ohio.
In addition to the possible brawl at the convention, major conservative donors who have planned to bankroll issue-oriented advertising and other grass-roots efforts directed at social conservatives are putting their work on hold and will withdraw financial support if McCain picks a running mate that is not strongly anti-abortion, sources told ABC News.
One conservative strategist characterized the prospect of an abortion rights pick as a "disaster" for the Republican Party -- and said selecting Lieberman would cost McCain the election. It would enrage conservatives and prompt some Republicans to shift support to libertarian candidate Bob Barr, the strategist said.
With the election so close, even a couple percentage points could make a difference.
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McCain told a Pittsburgh radio station this morning that he had not made a final decision, though sources within his campaign later reversed that claim.
This morning, sources told ABC News the timing of McCain's announcement had not been finalized -- and would not be settled until McCain made his choice. They said at the time that the pick could be revealed on Saturday or closer to the opening of the convention next week.
Two pro-abortion-rights contenders remain very much in the mix: Lieberman, who was Al Gore's Democratic running mate in 2000, and former Pennsylvania Gov. Tom Ridge. Either would mark the first time in modern history that an openly pro-abortion rights candidate for vice president was on the Republican ticket.
McCain also is considering Minnesota Gov. Tim Pawlenty, a popular two-term governor in a moderate state who would bring blue-collar roots and Ronald Reagan conservatism to the ticket.
The 47-year-old Pawlenty, who is an anti-abortion rights advocate, is in many ways the conservative version of Obama, but with executive experience: same age, similar backgrounds, same law school education and careers in public service. As governor, Pawlenty erased a deficit and balanced the budget while pushing through conservative programs.
McCain also is considering his former bitter rival Mitt Romney, a multimillionaire businessman who would bring economic experience but who was also harshly criticized by the Arizona senator and social conservatives during the primaries.
Romney, who is an anti-abortion rights advocate, was seen as flip-flopping on key social issues in a perceived effort to pander to the Republican base. Moreover, Democrats are already painting Romney, with his $30 million in residential real estate and offshore tax havens, as elitist and out of touch with everyday Americans.
As McCain contemplates his choices, he is deciding between the conventional conservatives like Pawlenty and Romney and the two pro-abortion rights picks, who could perhaps open the party to moderate voters who backed Hillary Clinton in the Democratic primaries.
Before the Democratic National Convention, polls showed that 30 percent of Clinton's 18 million votes were up for grabs -- they had not decided whether to shift their support to Obama. The McCain campaign has aggressively courted those voters with a series of television ads running this week to coincide with the Democratic convention.
Ridge and Lieberman, it's believed, could appeal to some of those voters. Ridge would help in Pennsylvania, a key swing state. And Lieberman would enforce McCain's reputation as a political maverick who has a history of building bipartisan coalitions.
Both men are close friends with McCain and have appeared frequently on the campaign trail with him, and both share his views on national security.
And both would trigger a brawl at the convention next week in St. Paul, Minn., the likes of which hasn't been seen at a Republican gathering since the 1964 nomination of Barry Goldwater, the last Arizona senator to be the party's standard-bearer.
"I see a fight at the convention over either," said Phyllis Schlafly, president of the Eagle Forum.
The choice of Lieberman would trigger an all-out war. Although he supports the war in Iraq and is therefore considered by some to be a "moderate," he has liberal views on social issues deeply important to the Republican base. He has taken positions at odds with the party on gun control, tax cuts, gay rights, abortion and the Supreme Court, including voting against conservative Justice Samuel Alito.
"There would be a major revolt if it were Lieberman,"said Schlafly. "I just do not believe the Republican convention would nominate Lieberman. I just don't think they would accept it, no matter if McCain wanted it."
Ridge, too, would also trigger a fight because of his views on abortion rights, although he is more conservative on other issues important to the base.
Charmaine Yoest, president and CEO of Americans United for Life, said either pick would be deeply disappointing for the anti-abortion rights base and would bring disarray to the convention next week.
"There's been a lot of talk about what kind of response there would be. The worst thing that you can have at a convention that's supposed to be a party is to have people anxious to leave. You'd see people who weren't willing to wave signs. You'll see people sitting on their hands, looking at their watches and real, real disappointment.
Yoest said the anti-abortion movement was energized after McCain's "strong performance" talking with evangelical leader Rick Warren at his Saddleback Church and were pleased with the strong platform the delegates had just approved.
"There's an expectation of wanting to see the platform and the ticket match, and for there to be the same enthusiastic commitment to life," she said. "The mental image of placards being handed out at the convention for a candidate who stands for abortion -- instead of life -- just doesn't work."
No modern Republican presidential nominee has ever campaigned with an openly pro-abortion rights running mate. In 1980, Ronald Reagan tapped George H.W. Bush as VP, despite Bush's past opposition to a constitutional amendment to ban abortion -- but he didn't give him the spot until Bush agreed to fully embrace the anti-abortion rights agenda.
"It would be a terrible mistake. Every one of our nominees has been pro-life," Schlafly said. "It's sticking his finger in face of the pro-life constituency to pick someone who isn't pro-life."
Although Ridge has indicated in recent interviews that he would support McCain's policies, he has not said he would repudiate his pro-abortion-rights views. Lieberman not conceded that; he has been a strong advocate of abortion rights, repeatedly earning an 100 percent approval rating from abortion-rights groups.
Social conservatives are now planning their strategy to block either potential pick.
One possible strategy is a revolt by some of the 18 state delegations who supported either Mitt Romney or Mike Huckabee -- and who have not yet turned over to McCain.
Those delegations could -- and sources say, likely would -- revolt against Lieberman and put in their own VP recommendation. To be nominated, a candidate needs five delegations to support the nomination.