Usually this allegiance is given by the promise to fulfill their particular intrepretation of the Bible. All that makes the news seems to be abortion and homosexuality, issues that must be engaged, but often at the expense of the rest of the Bible's teachings. Often times Christians in opposite parties, in a reactionary way, totally ignore the pet issues of Christians in the other party, no matter the Biblical justification.
By sticking with one party, Biblical teachings will be compromised. There is no way around that. Christians who align themselves with Democrats yet are against abortion may sometimes feel unwelcome at party gatherings. Likewise, Christians who identify with the GOP may not speak out, or worse, champion the excesses of the corporate wing of the party.
Today in the church, too often the Old Testament and Prophets are at best ignored and at worst maligned. In Jeremiah, we know that God is not happy with His people, but often times the reason why is not explored, or Jeremiah is merely used as a tool to point to Christ or the an apocalypse. Jeremiah's temple speech commands that:
For if you truly amend your ways and your doings, if you truly act justly one with another, if you do not oppress the alien, the orphan, and the widow, or shed innocent blood in this place, and if you do not go after other gods to your own hurt, then I will dwell with you in this place, in the land that I gave of old to your ancestors for ever and ever.
Amos goes on to proclaim "Seek good and not evil, that you may live; and so the LORD, the God of hosts, will be with you, just as you have said. Hate evil and love good, and establish justice in the gate;..."(5:14-15a).
Of course the prophet Micah reminds us that "He has told you, O mortal, what is good; what does the LORD require of you but to do justice, and to love kindness, and to walk humbly with your God?"(6:8).
We know that God judges and that he abhors sin, but we cannot simply gloss over those teachings of the Old Testament. If we are to believe in the entire Bible, we must wrestle with these commands and not simply dismiss them with some sort of convienent theology.
Likewise, we must have the courage like the prophets and boldly proclaim what God commands us to say and do. Sure the prophets are immortalized in the Holy Bible forever, but they were not especially popular people back in their time. Even when Jerusalem was under siege, Jeremiah was in jail because he was considered a traitor for suggesting that Judah would pay for its sins.
God cannot be confined to one political party. The Bible cannot be the sole property and interpretation of one political party. Why has this happened? My layman's view is that it's too easy - vote at the polls for the politicians that speak your language and God will be pleased. There's no committment, no cross to bear, no narrow path - just show up at the polls once every other November and your duty is done.
I would love for someone to point out in the Bible where it says that following God is easy. The Bible was not dropped from heaven as some sort of rulebook or clear-cut guideline - we have to wrestle with all the teachings and understand what they say. We cannot pick and choose abortion and homosexuality or focus only on poverty and the suffering - if we say we believe in the Bible, we must read it with an open mind to see what it really says, and not what we want it to say. We must read the entire Bible, or else we pervert what God may be actually saying by attempting to think for Him.
We must engage all the issues and not sell out Biblical teachings so that we may curry political favor. I pick mainly on the GOP because they're currently in power, and we've witnessed how power can corrupt (which is another theme in the Old Testament that's routinely ignored, but we'll save that for later). Else, we may ignorantly find ourselves committing the same errors as the ancient Israelites which drew God's wrath.