Official political innumeracy, enshrined in the census, steals our democracy. We count illegal immigrants the same as citizens and assign states congressional seats accordingly. This awards some states more representatives than they deserve. The census should, instead, count citizens separately, and Congress should reapportion representatives only on the basis of citizen populations. That would ensure that the votes of citizens in all parts of the country are as nearly equal as possible.

Although this largely unrecognized problem doesn't garner headlines, the failure to fix the census may have greater consequences as our political realities change. The unpleasantness in Arizona since it passed a tough immigration law is a likely prelude to infinitely more divisive conflicts.

The Constitution contains a mandate for a census. One of its stated objectives is to enable the proper apportionment of representation, state by state, in the House of Representatives. From the start, however, apportionment has been a mangled affair, a stain on our claim to be a true and fair representative democracy.

The deal worked out in Philadelphia in 1787 counted slaves as three-fifths of a person, even though they could not vote. The third U.S. Congress, meeting from 1793 to 1795, relied on the census of 1790 to apportion its 106 House members. Southern slave states were overrepresented by 10 seats as a result, after applying the three-fifths rule. No one even pretended that the slaves who accounted for those extra seats had any representation at all. The consequences of such unfairness proved catastrophic.

The Civil War settled many issues, but democratic apportionment in Congress was not among them. In fact, the disproportion was made worse by the 14th Amendment, which allowed former slave states to count their now-freed Negroes without the two-fifths reduction. Negroes in the old Confederacy would account for even more Southern seats in Congress, yet they would not see their right to vote enforced for another full century — until the 1965 Voting Rights Act.

Congress remained true to the Constitution, regularly increasing the number of seats in the House based on census results from 1790 through 1910. But for the most part, no additions have been made in the 100 years thereafter.

The reapportionment of today's static 435 seats according to census results would be a respectable example of representative democracy if each individual included in the count had a vote. But the system remains badly fractured and fundamentally unfair. Worse yet, to the extent that the census accurately counts illegal immigrants, the greater the disproportionate representation accruing to states with large illegal communities, which cannot vote.

Adding to the complexity of the problem, in states that gain such seats, many fewer votes are needed for a candidate's election. That's because the added seats mean there are fewer residents in each district and, in the districts with the highest number of illegal immigrants, fewer eligible voters. We do not know empirically whether these "cheaper" votes carry any political bias, but it is not unreasonable to worry that they do since the illegal immigrants counted who created the new seats are not represented by the eventual occupant in Congress. None of this is fair, in either the local or national context. And the 2010 census is sure to aggravate the situation. We should do something now to prevent this.

To be prudent, we should also consider a not implausible, worst-case scenario. Suppose that the Mexican government collapses, sending hundreds of thousands of refugees across the border. Those who manage to stay will be counted in a future census. States composed of mostly citizen populations would lose representation and quite rightly feel cheated.

The present potential for disaster, for severe damage to the principles of democratic representation and for the future of the republic itself should be a paramount concern for all Americans. The good news is that the Constitution leaves the manner of conducting the census, and the apportionment of the House, up to Congress. Passing a census reform law should be a relatively simple fix, if we have the leadership and the will to do so.