(keeping in mind that I am not a Christian myself, so the tongue-in-cheek aspect is a bit stronger here than in the matching argument given in 'Donkeys and Elephants
' about the Pledge of Allegiance being contrary to republican values and freedom of conscience.)
Can a Christian, in good conscience, pledge allegiance to any secular power, and if so, to the US specifically?
Despite the claims of some of the 'Religious Right', the US Constitution does not have it's legal and moral basis in Christianity; indeed, while several of the original colonies were founded by religious groups, the reason they came to the US was to escape the religious strife that was at the time setting Europe ablaze; for exmple, Maryland was originally settled by English Catholics who were forced out by the Anglican Church. As the colonies grew into the semblance modern form, they all agreed on one thing: that a state church was wrong, and that the only way to avoid strife was to avoid state religion.
As the 18th century Enlightenment developed, the idea that one needed to be religious - or at least, part of an organized religion - came to be questioned; the Founding Fathers were almost all Deists - holding that religious faith (or lack thereof) was purely personal - and most of the had accepted the Newtonian idea of clockwork universe. This isn't to say that they weren't religious or Christian themselves, though they often had very unorthodox beliefs, and shown by Thomas Jefferson's version of the Gospels
: he edited them to emphasize the ethical teachings he felt important and genuine, while removing all reference to anything supernatural or miraculous, including the Resurrection itself. His Joshua ben Joseph was a great moralist and philosopher, but nothing more, in keeping with Jefferson's "Nature's God" whose creation is a finely crafted machine.
US law is also secular, and it's basis is less in the 'Ten Commandments' (which of the three sets of laws under that name would it refer to, anyway? Taken as a whole, Talmudic law is quite inconsistent, and in any case, the 'new covenant' is supposed to set those laws aside in favor of 'love thy brother' as the only moral and legal stand, anyway) than in Roman civil law; the entire idea of judicial precedent and the authority of law goes against the Biblical view of justice, which held that Judges were to follow divine inspiration rather than written law.
Also, the US, and all modern democracies, hold pre-emminent the ideal of 'freedom of conscience', both in religion and politics. This ideal assumes that all points of view are equally valid, or at least should have the right to compete, market-style, for support. The ultimate expression of this is in the democratic process itself: everyone, or at least every adult citizen who isn't a criminal or insane, gets a voice, with the loudest voices winning but the smaller ones, if not hear, at least nominally protected from reprisal.
Can this be reconciled with the tenet that 'only through Christ can you find salvation'? Different sects may tolerate each other to some degree as a practical matter, but in the end, don't they all hold that heretics - that is to say, any one Not Us - is damned? How can their be 'freedom' to deny the only right path?
For that matter, how can there be 'individual conscience', anyway? The laws of God - whatever you may see them as being - are absolute, and by nature, arbitrary; I AM THAT I AM has no obligation to explain Himself to His creations, or even to comprehensible to them. To a faith-holding Christian, the Law of God is just that: it cannot be appealed to, revised, or re-interpreted, except by Him (indeed, the idea that even He would ever do so is one of the reasons most Jews rejected early Christianity - it implies that He is fallible and inconstant). The Kingdom of Heaven is just that: an autocracy. To claim that one can choose their laws - even their secular laws - flies in the face of this, and shows a level of hubris that is very un-Christian indeed.
In the end, one can believe in democracy (or republicanism, in the sense of 'the republic'), or in Christianity, but not both.
And now we come to the reason I bring this up: it means that Theocrats like Dubya and Robertson are playing us a crooked hand. Either they haven't understood the implications of their own claimed positions, or else they are misrepresenting their real views. Which is it?
Do You Believe That? (TM)