The Supreme Court will rule, perhaps before July, on the constitutionality of restrictions on political communication imposed by the 2002 campaign finance law (McCain-Feingold), the premise of which -- substituting concision for precision -- is that there is "too much" money in politics. And crusaders for campaign finance restrictions profess themselves scandalized by the fact that spending by candidates, parties and interest groups in the 2001-2002 election cycle on the principal means of political communication -- television advertising -- totaled almost a billion dollars ($996 million).

But that is exactly what Americans spend every two years on pork rinds. So the interesting question is "Why Is There So Little Money in U.S. Politics?" That is the title of a paper, soon to appear in the Journal of Economic Perspectives, by MIT professors Stephen Ansolabehere, John de Figueiredo and James M. Snyder Jr. Their analysis is pertinent to the argument about constitutionality.

The Supreme Court has held that limits on campaign expenditures are more difficult to square with First Amendment protections of political advocacy than are limits on campaign contributions, and that limits on contributions are justified only as remedies for corruption or the appearance thereof. Reformers assert or imply that private campaign contributions are inherently corrupt. This is because the reformers, substituting moral fervor for empirical evidence, assume that the primary motive for most contributing is what economists call "rent-seeking" -- the purchase of policies favorable to the contributor. Ansolabehere, de Figueiredo and Snyder shred that assumption.

There are hundreds of candidates for federal offices seeking funds, and scores of millions of individuals and hundreds of thousands of businesses and other interests affected by government action. The federal budget is approximately $2 trillion, and government regulations of all sorts have a monetary value of many additional hundreds of billions. So why was only $1 billion -- a pittance, relative to the stakes of government policy -- spent in this election cycle by candidates, parties and interest groups on the most important form of political communication?

Ansolabehere, de Figueiredo and Snyder answer that the huge discrepancy between the sum of contributions to politicians and the total value of governmental actions points to an explanation of political contributing other than rent-seeking. Their explanation is that "campaign contributing is a form of consumption, or, in the language of politics, participation."

Most political money -- about 80 percent -- comes from individuals, and in relatively small sums, which strongly suggests that the contributors cannot expect significant private benefits from swaying policy. Rather, the satisfaction of participation is a sufficient explanation of political contributing, as it is of contributing to charities.

And individuals who make political contributions "are also disproportionately likely to participate in other ways." Such individuals give because the consumption/participation is ideologically or socially satisfying or exciting. Furthermore, "consistent with the notion that campaign spending reflects participation, trends in aggregate spending over the last 100 years are explained entirely by growth in personal income."

The authors argue that if rent-seeking explained contributing, then contributing should rise as a function of total government spending. However, if the consumption/participation model explains contributing, then contributing should be a function of personal income, and of the competitiveness of particular races. Which is the case.

Although the growth of the regulatory state in the 20th century made government vastly more important as an allocator of wealth and opportunity, campaign spending as a fraction of national income did not grow during the last nine decades of the 20th century. That is, it did not grow after the coming of the secret ballot and civil service and other reforms that weakened the vote-buying powers of political machines. This, the authors say, "suggests that the private benefits bought through the campaign finance system are not an increasing problem for our economy."

The consumption/participation model explains why political contributing, like charitable giving and consumption generally, increases with per capita income rather than with the value of government activity. It also explains why political contributing by rent-seeking interest groups is so small relative to the monetary value of government action.

The authors' study of legislative decision-making accords with the extensive social science literature that concludes that legislators' voting is almost entirely a function of their own beliefs and the preferences of their voters and their party. The authors say that "after controlling adequately for legislator ideology, [interest group] contributions have no detectable effects on legislative behavior."

The Supreme Court should consider this when assessing the constitutionality of a law based on the bald assertion of "corruption" resulting from "too much" money in politics, a law that suppresses political participation.