It's interesting, and more than a little bit disturbing, just how often conseravtives and Republicans claim that God is on their side politically -- that their policies, their politics, their agenda, and even their political party are specifically favored by God. Many people recognize it as a sign of extreme arrogance and hubris to imagine that God is taking one's side in the political realm. This tactic is much more, and much worse, than mere hubris though. It is also an attempt to undermine the democratic process itself.
Democratic politics involves different people with different interests, ideas, and even values reaching common ground on how to govern a community. The process of democratic governance must be human-oriented because it's a process of creating human compromises in the service of human interests. People may bring values and ideas derived from religious belief systems to the table, but the decisions cannot be religious in nature and still remain truly democratic.
Claiming that one is acting on behalf of God, and that God specifically favors one's policies, circumvents all this. The implicit assumption is always that God's wishes and agenda cannot be compromised on. They cannot be the subject of debate, disagreement, or dissent. They cannot be set aside in favor of some other policy. To claim that God favors just one side is, then, the rejection of the democratic political process by which laws and policies are normally formed.
It's not just a rejection of any possible compromises for the sake of others who have different interests, but also a rejection of the possibility that an entirely different policy might be preferable. There is no need for any investigations into the consequences of the policy or whether the policy will actually achieve the stated objectives. There is no need to look at whether some other policy would do a better job. Once God has spoken, all debate must end.
When someone says that God is a Republican, they are denying legitimacy to any non-Republican positions. When someone says that God favors a particular Republican policy proposal, they are denying legitimacy to any democratic process of debate and compromise over the issue. They are thus seeking to have the policy imposed in an anti-democratic manner. They are seeking the power to rule over others without having to be answerable in a democratic manner.
This image is based on a Nazi propaganda poster.