Political opinions are always best left to individuals. No one can really say if someone should be a republican or a democrat. Christian and republican agendas seem to be more in line than democrats and Christians, simply because republicans are more traditional and old fashioned. They both tend to like things as they were and are generally against most kinds of change, whether politically or religiously. Having said that, there are many people who are Christians and are democrats as well.
It usually comes down to a belief in marriage and whether homosexual people should be allowed to marry. If you answer that question, you will likely find what political party you should belong to.