The key phrase here is some circumstances. The Aboslutely no abortion whatsoever anytime, anyplace under any circumstances crowd is not a large constituency.
Most people at the very least would support emergency abortion if the mother's life is in dire peril. And I'd bet money that no less than 50%+1 of the adult population supports elective abortion during the first trimester of pregnancy.
Many of these folks vote Republican. A few even post on this forum.
Actually, I wouldn't be surprised if it was higher than 73%. Or, to put it another way, I wouldn't be surprised if fewer than 27% of people would oppose the removal/destruction of an embryo/fetus which was implanted within the fallopian tube. There is at present no technology which can rescue such an embryo/fetus, and the only course of action to minimize severe risks to the mother is to remove it as soon as practical.
On the other hand, I would be very surprised if even 50% of Democrats favor allowing child molesters to have the evidence of their crimes anonymously disposed of in abortion mills. Any effort to stop such things, however, is met with loud howls by PP et al.
What universe does this 73 percent exist?
Sadly, that is probably not as wrong as many here seem to think. I think the vast majority of REPUBLICANS (as opposed to true-blue conservatives) do favor abortion in some circuimstances. Whether it is 73 percent or not, I do not know, but if I had a dollar for every time I heard or read "I am against abortion, except [but]..."
Polls show that 73% of what anyone at Planned Parenthood says is a lie.