Why DOes McCain have A Problem with Pro-Lifers and Romney Does not?

This seems to be the meme I keep seeing. I know McCain has big issues on Stem Cell research. That being said I keep hearing " Well we Social Conservatives just don't trust McCain". I am curious why just four years Romney was a very pro-choice governor seems not to matter?

The problem with Romney was it was never clear if he truly believed this stuff he was spouting. I mean fours years he was singing a different song and dance to pro -choice supporters.

I just want to point this out since I suspect now the ROMNEY movement for VP is going to be in full force now.