Today’s Supreme Court decision in the Citizens United case is a disaster for the American people. It will unleash unprecedented amounts of corporate “influence-seeking” money on our elections and create unprecedented opportunities for corporate “influence-buying” corruption.

In a stark choice between the right of American citizens to a government free from influence-buying corruption and the economic and political interests of American corporations, five justices came down in favor of corporations. Chief Justice Roberts has abandoned the illusory public commitments he made to “judicial modesty” and “respect for precedent” to cast the deciding vote for a radical decision that profoundly undermines our democracy.

The constitutionality of the corporate spending ban was never even raised by the plaintiffs in the lower court consideration of this case. Instead, the justices, on their own, opened up the case to the broader constitutional question, when they could have decided the case on narrower grounds without eliminating more than 100 years of national policy.

Instead, the court’s majority overruled cases decided in 1990, 2003 and 2007, without any changed circumstances to justify these abrupt reversals. The only change that has occurred is a change in the makeup of the court itself. The damage to electoral democracy will be substantial.

The Fortune 100 companies alone had combined revenues of $13 trillion and profits of $605 billion during the last election cycle. Under today’s decision, insurance companies, banks, drug companies, energy companies and the like will be free to each spend $5 million, $10 million or more of corporate funds to elect or defeat a federal candidate — and with that power, influence the candidate on issues of economic importance to the companies.

Congress and presidents past have recognized this danger and signed numerous laws over the years to prevent this kind of corruption of our government. These laws have consistently been upheld by the Supreme Court until today.

In the coming weeks, Congress should explore all possible legislative options to deal with the consequences of this decision. The case reinforces the need to repair the presidential public financing system and create a new system of congressional public financing, and to make small donors the key players by providing public funds to match small contributions.

Justice Louis Brandeis once said, “The most important political office is that of the private citizen.” Today’s Supreme Court decision rejects Justice Brandeis’s view, raising corporations to new heights of importance in our political system.

-- Fred Wertheimer is the founder and president of Democracy 21, a nonpartisan, nonprofit organization that works to promote campaign finance reform and other political reforms. He is a lawyer on the amicus brief filed in the case by the Campaign Legal Center and Democracy 21. Mr. Werheimer's piece originally appeared on NYTimes.com.