There are threads at Bitch and Majikthise about whether abortion rights should be a "core issue" or even a "litmus test" for Democratic candidates. Much of this was sparked by the decision of NARAL to endorse pro-choice republican Lincoln Chafee.
I'm not ready to contribute a full post to this issue, but I do want to relate the story of the one time I voted for a Republican.
It was the governor's race in Illinois, and a conservative, downstate democrat was running against a liberal republican. I was a Chicago resident at the time, and the thing that pissed me off most about the conservative Democrat was the fact that he was in bed with the NRA. Here was a guy from a rural area promoting the gun trade, which didn't hurt his constituency much, but killed people every day in Chicago. It was really an upwind/downwind issue. People who live upwind from the factory don't mind the smog. People who live away from cities don't mind the gun trade.
Gun control turned out to be my litmus test. I didn't think of myself as a single issue voter on gun control. But in this case, it was the one that did it for me.
I don't remember where either candidate stood on abortion.
The Republican I voted for was George Ryan. He won, and left a complicated legacy. On the one hand, he placed a moratorium on all executions in Illinois. His last act as governor was to commute the sentences of everyone on death row. On the other hand, he got caught up in a nasty bribery scandal dating from his days as secretary of state.
I still feel like I made the right choice.
Update: The Nation has a peice on why gun control is the issue democrats should give in on. Interestingly, the proposal doesn't seem to simply be compromise, but completely dropping gun control from the agenda. Because, you know, we can always count on the cities to vote Democratic.