Though it has begun in earnest, the presidential race is not yet serious. It's still in that early stage when the candidates introduce themselves on the basis of their biography and the offices they've held, as if they were running for student body president. There is no significant policy debate.

Enjoy it while it lasts. The contest's next phase has a way of reducing the candidates to policy wonks, especially the Democrats, who in order to mobilize their disparate supporters must advance long, specialized agendas. Goodbye, "the audacity of hope." Hello, the hope of audacity, of any sort of bold Democratic policy addressing the common good rather than client groups.

Republicans have a hard time competing against such pandering, but that won't stop them from trying. The best way to avoid this race to the bottom is to connect Republican policies to the Constitution and its principles. Thinking about the Constitution as a guide to policy has almost gone out of style, except in the appointment of judges and the current debate over war powers, a welcome throwback, in its way. One would have to go back to the Reagan era, and before that to the 1960s, to find Republican leaders opposing major government programs on constitutional grounds.

But the alternative to reviving constitutionalism is to make policy with no limits except for the judges' whims, and with no guide except our leaders' visions, distilled from their constituents' desires. The alternative to constitutionalism, in other words, is to play politics according to the Democrats' rules. That's a losing game.

Here are some issues where conservative candidates might start to change the rules and play a winning game, beginning with national defense. Granted, you cannot deduce defense policy from the Constitution, but it does convey a sense of priorities and the means (an energetic executive) to pursue them.

National defense is the national government's most urgent and fundamental priority. But as Robert Samuelson noted recently, defense spending is only a fifth of the federal budget; in 1956, during a peaceful part of the Cold War, it was 60 percent of the budget. Social welfare spending (counting Social Security and Medicare) has moved in the opposite direction. It was a fifth of the budget in 1956; today, it is three times that percentage, and climbing. While waging a multi-front war, the Bush Administration has done all it can to hold down defense spending and the size of the armed forces. Partly, this is the result of its faith that with high technology and transformed forces, more could be done with less. Partly, however, the administration fears being backed into a tax increase, or unpopular reductions in spending, or both.

But conservatives ought to do better than that. National defense is central to constitutionalism in a way that entitlement spending is not. Defense spending needs to grow dramatically, and if that forces a hard look at entitlements and domestic discretionary spending, all the better.

Or consider abortion. Conservatives favor overturning Roe v. Wade. Even Rudy Giuliani, who says he favors appointing "strict-constructionist" jurists like John Roberts, Antonin Scalia, and Samuel Alito, therefore implicitly favors overturning Roe, despite his professed belief in a woman's "right to choose." If it overturned that arrogant decision, however, a strict-constructionist Supreme Court would not replace it with a new, judicially created regime outlawing abortions; in all likelihood it would return the issue to the state legislatures.

Conservatives should talk more about the constitutional outcome they seek by invalidating Roe. In essence, they favor a return to the status quo ante, in which abortion is primarily a matter of state law. This federalist outcome would mean that Iowa and South Carolina would not have to have the same abortion law as New York. Abortion would be illegal in some states, legal in others. Though not ideal, this situation is morally and politically better than the current thralldom to abortion on demand, and it does not preclude continued agitation for the Human Life Amendment or its equivalent.

By emphasizing federalism as the way forward on abortion, conservatives would emphasize their own constitutional fidelity and moderation, redirect our court-centric politics, and undermine the Left's doomsday fear-mongering.

A constitutionalist agenda would embrace other conservative causes, but it would change the tone, and to some extent the substance, of the arguments. In addition, it would raise new issues to the fore. Will future citizens revere the Constitution as they should? Will immigrants regard it, and the language in which it's written, as focal points of civic unity?

Bringing the Constitution back would at least lend the 2008 race a presidential seriousness and focus. The new occupant of the Oval Office will swear, after all, to "preserve, protect, and defend the Constitution of the United States."