National Right to Life's Dave Andrusko provides some background and digs through the Public Religion Research Institute's poll on abortion, etc.
Besides his points, I think it's important to point out how a large percentage of the public seems to either be heavily conflicted on the abortion issue or just respond how they think the pollster wants them to respond based on the question.
Question 11 in the survey asks: "Thinking about the purpose of abortion laws please tell me whether you think it is appropriate or not appropriate for these laws to do any of the following."
Then 4 different purposes are randomly given and the pollster asks, "Is it appropriate for abortion laws to do this or not?"
One option is (my emphasis): "Protect the life of the fetus throughout the entire pregnancy."
63% of people reply it's appropriate for abortion laws to protect the life of fetus throughout the entire pregnancy.
Another option is "Preserve a woman's freedom to make her own decision."
70% of respondents found this appropriate.
You're not crazy if you think that doesn't make a shred of sense. You have roughly a third of respondents taking the completely opposite position on abortion laws from a position they took a couple seconds ago.
Second, large percentages of the public are extremely ignorant on the reasons why the majority of women have abortions.
In Question 6, 56% of respondents say abortion should be legal in all (19%) or most (37%) cases. But when asked later in Question 10 if abortion should be legal in certain circumstances, respondents are much more likely to say abortion should be illegal in the circumstances that are the most common reasons for abortion. 52% of respondents said abortion should be illegal "if the family has a very low income and cannot afford any more children."
You won't hear pro-choice groups yelling that result from the rooftops.