There are some things that are varying shades of gray, but there are also black and white.
When I start talking politics with people I explain that I am not a party line person. I actually test out as a Libertarian, and in following those in office it is confirmed. I stand firm that everyone needs to look at the issues and rate them against their own philosophy: What are the likes and dislikes, what are important and not so important, and what are the drop dead issues (you can't have more than one of these, so you need to look at is as a class or items).
To me a drop dead issue is make or break, and I won't cross the line on it. Important is almost as strong, but if I am going to accept compromise I do it in who I chose, not how I will expect them to give away, and likes and dislikes are frills that don't really matter - Colored lights decorating the White House, brown shoes with black suit, number of flags on the stage or a flag pin on the lapel.