That's because the two belief systems are mutually exclusive.
Christians are pro-life, anti-homosexual behavior, pro-family, pro-America.
Democrats (as defined by the national platform which ALL democrats support (else they would change parties)) are pro-abortion, pro-homosexual behavior, anti-family and anti-America.
So if someone claims to be both Christian and democrat they are lying about either being a Christian or about being a democrat. And since the democrats are the party of liars it's a pretty good bet they are lying about being Christian
(There is one exception to this, that is the person whose daddy was dem and whose grand daddy was dem and therefore they are dem. They believe in conservative values but still vote dem due to tradition. I'm not sure if these folk can be Christian as I'm not sure they have the mental awareness to be able to make that decision)
What about those with split views? Quite a few voters are conservative on economic and foreign policies but liberal on social policies and sit in the Republican Party. Are they Christians?
Also many voters are liberal on economic and/or foreign policies but conservative on social policies, and many of them are in the Democratic Party.
Also the Democratic platform was by no means approved by all the delegates, just like the Republican platform had dissenters as well.
Thanks John. Good comments. I agree.