Christians As Earthly and Heavenly Citizens

What is the relationship between our heavenly citizenship and our earthly life? According to Scripture, how ought the fact and privileges of our heavenly citizenship influence our earthly citizenship involvement? How do we go about weighing the ethical merits of two candidates when both have morally questionable features? Should the church be involved in politics? Is it possible for a biblical Christian to support the Democratic Party? Is a third-party vote a reasonable choice in this particular election? Is my vote more of a simple or a complex decision? How can I have a “clean conscience while voting in earthly elections?