The GOP didn't so much make abortion a wedge issue as much as evangelicals captured a big chunk of the party's lame duck platform during the various positional realignments of the 60s-80s. The GOP, by almost sheer luck, managed to stumble in to an apathetic voter block, and came out with one of the strongest, most long lived cores of voters out there.

The real strategic leadership of that block mostly died off in the 2000's though, leaving evangelicals headless and politically adrift. These days most seem to have reverted back to being somewhat apathetic in the positive direction, and aside from abortion, are voting completely based on the products out outrage culture.