Palin is an outspoken opponent of abortion, opposing the termination of a pregnancy in all cases except when the mother's life is in danger. Palin also opposed sexual education programs in schools, other than an abstinence-only curriculum, during her 2006 Alaska gubernatorial campaign.
Grover Norquist, the anti-tax activist who leads an influential weekly meeting of conservatives, reacted to the news that Gov. Sarah Palin's, R-Alaska, 17-year old daughter plans to keep the baby and marry the father by saying that the GOP's pro-life base is "over the moon" because it re-enforces that the Palin family lives its pro-life values.
"Before they were excited about her with the down syndrome baby," Norquist said, "but now with this, they are over the moon. It re-enforces the fact that this family lives its pro-life values."
Prominent conservative leaders voiced immediate support for the Palin family.
"They seem to be doing the right thing on both counts: having the baby and marrying the father," Chuck Donovan, the executive vice president of the conservative Family Research Council, told ABC News. "God bless them both."
Said Dr. James Dobson, president of Focus on the Family: "Being a Christian does not mean you're perfect. Nor does it mean your children are perfect. But it does mean there is forgiveness and restoration when we confess our imperfections to the Lord. I've been the beneficiary of that forgiveness and restoration in my own life countless times, as I'm sure the Palins have."
McCain's communications director, Jill Hazelbaker, said the senator was aware of the pregnancy but did not think that fact should disqualify the governor in any way.
"It was part of Governor Palin's vetting, but I want to be very clear we expect the media will afford Bristol and Governor Palin the exact same privacies that they have afforded candidates past," Hazelbaker said. "Bristol Palin -- is not running for vice president, her mother is."
She said the campaign decided to go public in part because liberal bloggers had been attacking the Palins by suggesting that Gov. Palin pretended to be pregnant to cover for her daughter.
"The liberal blogosphere spent the last 48 hours attacking Governor Palin, suggesting her child was not her own," Hazelbaker said. "We felt that it was important for us to not only protect Governor Palin but set the record straight about these lies."
Yet Palin's image may suffer further if more damaging revelations come out in the coming days and weeks. Also Monday, the McCain campaign confirmed that Palin's husband, Todd, was arrested and charged with driving under the influence of alcohol in 1986, when he was 22 years old and was dating Sarah Heath, his future wife.
Today Laura Bush, who will speak to the RNC tonight during its abbreviated opening day session, expressed her support for Palin.
The first lady's spokesman said Bush did not know about the Palin's daughter's pregnancy before it was made public today, but she said the Palins should expect the campaigning to be tough, adding "You have to be ready for politics as usual."
Republican strategist Rick Wilson said that if Democrats seek to make an issue out of the pregnancy or other aspects of the Palins' personal life, the attacks will backfire.
"American families don't all live in the perfect sitcom world. She's not a stock person out of the Washington, D.C., show. She's a real person," Wilson said. "This shows not only that the Palins are a real American family, with all the good times and the tough times families face, it shows that John McCain is an unbelievably stand-up guy by choosing her."
ABC's Teddy Davis and Steven Portnoy contributed to this report.