Christopher Blosser writes a detailed post taking on the meme that pro-life voters have been "duped" by the Republican party.
I've never really understood this claim -- perhaps in part because it's usually made by people with a vastly different set of political preferences from my own. Certainly, one can agree that Republicans have not achieved as much as one might have wished in regards to the pro-life agenda. However, to suggest that social conservatives are wasting their votes by supporting candidates who mostly support their agenda, in preference to candidates who militantly oppose their agenda, seems rather contradictory.
The claim also suggests to me a certain historical forgetfullness. It's worth remembering that when abortion first became a national political issue in the US, the pro-life movement did not have a clear home in either party. Indeed, early indications would have suggested a home with the Democrats, which had traditionally had a massive following among Catholic immigrants and other blue collar workers. Under Nixon, it was by no means clear that the pro-life movement was welcome in the GOP, and although Carter was somewhat pro-choice, he was sufficiently quiet about it not to chase off pro-life Democrats. It was not until 1980 with Reagan's election that it became clear that it was the GOP that would permanently take on social conservatives, and many socially conservative Democrats began to stream over to the GOP at that time.