All right I didn't want to get dragged into my something-hundredth abortion debate, but here's my take. As I've already said, abortion amounts to little more than a
distraction issue; a small wrinkle in the much more pertinent issue of health care. Far more could be accomplished by preventing unwanted or dangerous pregnancies in the first place than by attempting to ban abortion (look up the "Global Gag Rule" for an example of this). It is already an extremely rare procedure as it is, and it hardly qualifies as the most pressing life-or-death issue facing society today.
However since I mentioned it, let's look at what scripture says. First there's the 6th commandment, which when correctly translated says, "You shall not commit murder." Murder implies a malicious premeditated killing, not any killing in general. Now let's look at what else the Tanach says. Throughout the bible the standard of morality could not be called "pro-life" by any stretch of the imagination. The god of the bible has no problem advocating or carrying out murders, wars, genocide, infanticide, and yes even abortions. In biblical times human personhood was not granted until 1 month after birth, because infant mortality was so high. For more information, check out the passages in this article:
http://www.religioustolerance.org/abo_biblh.htm
So if people intend to use a selectively literal translation of the bible as a source of "morality" then they should be willing to apply the same standard to the rest of what the bible says. Likewise if abortion is tantamount to murder then we should also regard stillbirths and miscarriages as criminally negligent homicide. You cannot have it both ways.
Now here's the scientific aspect of it. Let me start off by saying that science cannot tell you whether or not abortion is murder, because that is not its role.
Science can however tell you that the clinically defined end of human life is the complete and irrevocible cessation of brain function. If the heart or lungs stop working, the person's life can be saved if they are restarted, because their role is to sustain the brain. If the brain stops working, it cannot be restarted. Therefore if the end of human life is the end of brain function, then the beginning of human life is the start of brain function. A zygote does not have a working brain, whereas a fetus is born with a working brain, so we know it starts at some point in between. This time is around the third trimester, which in fact is the same exact time that the laws in most places already restrict the termination of pregnancies. On the other hand if human personhood is granted to a zygote then it should also be granted to eggs and sperm, because the potentiality for it to develop into an infant is there in all cases. You cannot have it both ways.
Science can also tell you that just as there is a direct continuum of developmental changes between a zygote and a human infant, there is a direct continuum of ancestral / evolutionary changes connecting modern humans to the common ancestor we share with our closest living relatives, chimpanzees. So science can't tell you whether abortion is murder. However it can tell you that if abortion is regarded as murder, then the killing of chimpanzees should also be regarded as murder. You cannot have it both ways.
Since this particular topic is about the policies and leadership of president Bush though, the debate over whether or not he is "pro-life" is rather moot at this point considering his positions on the Iraq war, capital punishment, and health care.