Some of these Christian friends and brethren will attempt to bolster their persuasive argument with appeals to Scripture. And, of course, it is true that the Scriptures are our rule not only of faith, but also of life. The Bible is not just a book that describes "religious things." The Scriptures do speak to issues of how countries are to be governed, and they do address many issues that are highly politicized. It's good and proper for Christians to appeal to Scripture to decide legislative and political questions. Those who suggest that the Bible is silent about such issues are wrong (and they are outside the boundaries of the Reformed confessions as well).
That said, just because the Bible has many things to say about legislation, politics, and so on, does not mean that the Bible speaks to every issue with the same level of clarity and does not mean that the Bible answers every question we may have. As others have pointed out, while the Bible speaks to all of life, the Bible does not provide the order of steps needed to rebuild a motorcycle engine.
So, when we are confronted with appeals to Scripture on these questions or any question where people are telling us that there is a divine rule, one question we should ask ourselves is "Does the Bible have a rule about that?" If the Bible does not have a rule, then we have Christian liberty to act within the broader and more general rules that the Scriptures provide.
So, for example, if someone claims that we must not vote for a Mormon or must not vote for someone who holds to black liberation theology, we may reply that the Bible has no such rule. I would probably disagree with aspects of what John MacArthur says (see what he says here), but he's right in saying that to an extent the question of selecting an elected official is a question of selecting an employee to perform a job.
Everything being equal, we would prefer to select a pair of employees that includes at least one Christian over pairs that respectively include a former Muslim and a liberal Roman Catholic or a Mormon and a conservative Roman Catholic. But not everything is equal.
The point of this post is not actually to persuade you, the reader, to join the mob I would like you to join. My goal is to encourage you to think clearly about the question of elections, to set aside scruples that lack actual Biblical basis, but to do so without forgetting that our acts as citizens must be in accordance with the rule of faith and life, the Holy Scriptures.
May the best mob win, but God's purposes will be accomplished regardless of men's machinations - political or otherwise.