Senior McCain campaign officials said McCain knew of the daughter's pregnancy when he selected Palin last week as his vice presidential running mate, deciding that it did not disqualify the 44-year-old governor in any way.
In the short period since she was announced last Friday, Palin has helped to energize the Republican Party's conservative base, giving the McCain camp fresh energy going into the campaign for the November 4 election against Democrat Barack Obama.
McCain officials said the news of the daughter's pregnancy was being released to rebut what one aide called "mud-slinging and lies" circulating on liberal blog sites.
According to these rumors, Sarah Palin had faked a pregnancy and pretended to have given birth in May to her fifth child, a son named Trig who has Down syndrome. The rumor was that Trig was actually Bristol Palin's child and that Sarah Palin was the grandmother.
A senior McCain campaign official said the McCain camp was appalled that these rumors had not only been spread around liberal blog sites and partisan Democrats, but also were the subject of heightened interest from mainstream news media.
"The despicable rumors that have been spread by liberal blogs, some even with Barack Obama's name in them, is a real anchor around the Democratic ticket, pulling them down in the mud in a way that certainly juxtaposes themselves against their 'campaign of change,'" a senior aide said.