I believe deeply the Church of Jesus Christ is called to embody and alternative politic. Politic defined as, simply, the way human beings live with each other. The Christian politic needs to follow the example of Christ, who, borrowing liberally from Philippians 2, did not consider power something to be used, but lived in weakness, suffered, and died. Through this counter-intuitive process, he was resurrected, vindicated, glorified. Christians believe this model is the purpose and intention of creation. Our politics must look like Christ.
It's also become pretty clear to me that Christians cannot faithfully critique any system they are trying to control. That doesn't mean we can't participate in systems of power, but we must be very careful not to attempt to control those systems.
Practically, that means in deliberative bodies - places like local or federal parliaments of one kind or another - that are genuine attempts to seek consensus and work together, align well. I'm comfortable voting for a representative of my community, if I feel they'll honestly engage this process and not seek to dominate or unduly influence the process.
When it comes to donating towards or working for the election of representatives from other constituencies, that's a clear attempt to control the process and, I don't believe, can be compatible with Christian ethics. The same goes for participation in "party" politics, where blocs of like-minded representatives seeks to influence the process. Any deliberative body must seek consensus - simple majorities overruling unwilling minorities are incompatible uses of power.
With regard to executive positions, where one person is expected to make unilateral decisions, I'm unable to envision a way to do this in imitation of Christ. If you had a genuinely compassionate, selfless human being, they would either be corrupted or fail as a government executive. Those jobs are not designed to be done in line with Christian ethics. I can't, in good conscience, put any human in a position where they cannot succeed.
Now, all of this does not mean I'd advocate disengagement from the process. Christians can and should still protest and express their views on how people should treat each other. The line must be drawn, though, in using threats or coercion to convince others of our positions. The example of our actions, we must believe, are capable of "winning converts," rather than the strength of our arguments.
It comes down to control. Am I attempting to get my way against the will of another. That's not how Christ operated; it's not how the Kingdom works; it's not how Christians can ethically engage in politics.
Our priority must be on the politics of the everyday. How do we treat our neighbors? Feed the hungry? Advocate for justice - not with threats, but with pleas to our common humanity?
If the life, death, and resurrection of Jesus Christ has both showed us how and enabled us to be truly human, capable of reaching our creative purpose; we must believe a Church, living in imitation of Christ, can facilitate the same transformation for the world at large.
God is in the business of redeeming creation. It does not come through force or coercion, but through humble, selfless love; a willingness to suffer; and a commitment to engage politics with an open hand and not a closed fist. It may also come in refusing to exercise "rights" we've been given as citizens of the world, because they violate the duties of citizens of Christ's Kingdom.