The above paragraph describes everyone who has honestly held a political opinion, ever. Everyone. Ever. Can we accept that much?
Now a favorite modern bogey-man is the idea that the "far right wing of American politics", whatever it calls itself at the moment and whatever it says its goals are, wants to impose a "Christian nation" scenario on the United States. In this rhetoric, the phrase "Christian nation" suggests, not merely that the nation as constituted pursue morals and policies consistent with a Christian ethos (which, for the record, is what most Christians in politics want, and the majority would likely be satisfied even with a consistent natural law ethic), but that the "Christian vote" wants to reconstitute America as a direct theocracy – or at best, a caricatured medieval-style polity where the church says what goes.
On any consideration, that caricature falls to pieces. Even the most hide-bound traditionalist Christian recognizes that this goal – even if any significant number actually have this goal – would falter on the simplest question of, "Which church?" The 1st Amendment was written to prevent that sort of authoritarianism. What the First Amendment doesn't say, however, is that an opinion is politically invalid just because it is religiously based. In fact, it protects the right to express your opinion: and bearing in mind the time period of writing, we have to realize that what the Founders were primarily protecting was religious, and religious political expression. Even if there were a vast conspiracy of loonies proposing to establish the rules of order of the Southern Baptist Church (or whatever) as the law of the land, they're completely allowed to say so: just vote them down.
As I mentioned, however, that's not what anyone – okay, almost anyone – is proposing. Politically active Christians, like anyone else who applies their beliefs to politics, think that their ideas are the best ones to put into practice. At the same time, almost all Christian politicians – it might even be fair to say especially Christian politicians – believe in working with the system of government as it is. If this means political movements largely made up of Christians want a "Christian nation" then we have to apply the same logic to other movements. Liberals want a "liberal nation". Neo-cons want a "Neocon nation". And so on and so forth. Communists want a "Communist nation".
If the ideas these groups advocate are goofy ideas, expose them as goofy ideas. If Christian ethics are goofy – I obviously think they're not, but then I'm Christian – then attack the ideas of the Christian ethics themselves. Debunk Christianity and its morals, if you can. But don't act as though it's ludicrous that Christians think Christian ethics are good for everybody: that's a logical fallacy from the ad hominem family. "Christians want an essentially Christian law code," is neither news nor a good reason to vote for or against such a code, any more than, "Homosexuals want a sexually free law code," is unusual or reason to vote one way or another on the subject.