Donald Trump's new policy prescriptions on illegal immigration, particularly on "birthright citizenship," have crystallized the terms of the debate among conservatives and indeed what it means to even be conservative.

To be truly conservative on illegal immigration now requires that you oppose birthright citizenship as it has historically been defined under the 14th Amendment. Trump, Scott Walker, Ted Cruz and others are taking stands on one side of that line; so far, Jeb Bush, John Kasich and Marco Rubio are on the other side. And when Bush has to inject a loaded term such as "anchor baby" into the discussion, as he did yesterday, you know that the shift has left him exposed and vulnerable.

All of which is driving more moderate Republicans to despair.

"It's a terrible idea. It's a politically insane idea. It can't be done. It's impossible to achieve," Peter Wehner, senior fellow at the Ethics and Public Policy Center and former official in the George W. Bush White House, told Politico. "So what's the point? It's symbolism and it's exactly the wrong kind of symbolism. If Republicans want to make this their symbol … they'll pay a high price for it."

He's right of course, at least when judged from a pragmatically political point of view.  There is no feasible means by which U.S. citizenship can be denied to those born on American soil. It simply isn't going to happen. And to the degree that such a policy becomes associated with the Republican Party, it ensures that outreach to the Hispanic community is doomed.  The RNC's post-2012 "autopsy" of the Republican loss to Barack Obama warned that "many minorities wrongly think that Republicans do not like them or want them in the country," and it's hard to conceive of a policy more likely to cement that perception than an assault on birthright citizenship.

But let's look at it another way. What if the fact that the policy could never be achieved is part of its attraction? What if the political price to be paid for that position isn't beside the point, but IS the point?

We've seen the dynamic play out for years now, and this is only its most recent iteration. If it looks as though the mainstream may be moving in its direction, the conservative instinct is not to reach out and meet it halfway and thus make policy gains. The instinct is to withdraw still further, to retreat from possible agreement and thus preserve the distance that defines it from the mainstream.

Thus, it's not enough any longer to merely oppose abortion. The once-standard conservative position has become more extreme -- outlawing abortion even in cases of rape, incest and to protect the life of the mother, with human life defined in all instances as beginning at the moment of conception.  That policy is a taunt of sorts to the mainstream: "Ha! Compromise with that!!" By taking that position, the line separating conservatism from the mainstream becomes even more impregnable, so to speak.

Such positions also serve as a test of group loyalty, a means of dividing "them" from "us." How to identify the fellow true believer from the moderate? By constantly raising the price of membership and seeing who will pay it. "Who will come with us?" they ask. "This is the new boundary, the line that divides us from them. Who will join us on this side of the line, and who will refuse?"

Viewed through that lens, what looks like an act of self-destruction from the outside is in fact self-preservation. What matters to conservatives is not the specific policy or position that is being rejected. What matters is the act of rejection itself. It is through rejection of the mainstream by conservatives, and the rejection of conservatives by the mainstream, that today's conservatism defines and protects itself.** So they court and provoke it.

In fact, you hear the same question being asked within the conservative movement all the time now, in various forms: How can we compromise with a world that we distrust and dislike, yet still remain separate from it? The answer for many is that they cannot. Compromise implies absorption and a surrender of identity, and thus must be avoided.

Let me quote again from that post-2012 autopsy:

"The Republican Party needs to stop talking to itself. We have become expert in how to provide ideological reinforcement to like-minded people, but devastatingly we have lost the ability to be persuasive with, or welcoming to, those who do not agree with us on every issue."

Again, from a purely pragmatic point of view, that makes sense if your goal is to expand the party's reach. But what if a significant portion of the Republican Party does not see that description as a problem for the party, but as a statement of the party's purpose? What if they want it to be a haven that provides ideological reinforcement to beleaguered like-minded people like themselves, and are willing to pay the price for that?

Wouldn't you get what we seem to be getting?

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** For example, Trump's most endearing quality to conservatives is his willingness to stick a finger in the eye of the mainstream, in blissful disregard for any consequences.