Because some voters do have one issue that is so important to them, they will not vote for anyone who disagrees with them on that issue. It's that critical a moral question to them.
Abortion is probably the best example, but there are others.
I think it is a pretty small percentage of conservatives, probably less than 5% on most critical issues, maybe a fair amount higher for abortion.
Not quite?
You mean you're open to supporting a pro illegal immigrant candidate if they happen to agree with you on other issues?