Three months ago, in a decision all but lost in the tumult over the Supreme Court's ruling on the Affordable Care Act, the justices overturned a century-old Montana law that prohibited corporate spending in that state's elections.

In the Montana case, the Supreme Court had the chance to revisit its deeply flawed 2010 decision in Citizens United. But despite the urgings of members of the court itself and a public shell-shocked by the recent torrent of unregulated corporate expenditures, the court chose instead to double down and reaffirm the conclusion of Citizens United that corporations are people, at least as far as the First Amendment is concerned.

As a legal decision, the Citizens United opinion was remarkable in many ways — in its willingness to overturn a century of jurisprudence, in its choice to issue as broad a ruling as possible, rather than as narrow as the case and Constitution required, and in its reliance on minority or concurring views in prior decisions, rather than the prevailing opinions in those same cases.

But what stood out most about Citizens United was not the court's legal reasoning, but its staggering naiveté. As the court confidently declared, “We now conclude that independent expenditures, including those made by corporations, do not give rise to corruption or the appearance of corruption.”

Well, glad that's settled. Unfortunately, the five justices who joined this opinion must be the last five Americans to feel that way. Certainly none of the evidence before the court in Citizens United or the Montana case compelled a conclusion so at odds with reality.

With the November presidential election fast approaching, corporate expenditures are now in the billions of dollars, and the “independence” of those expenditures — their theoretical separation from the office holders they are intended to influence — is a fiction no one buys. The proliferation of super PACs and their outsized influence on House, Senate and presidential politics is beyond dispute by all except those five Americans who happen to sit on the court.

But if the Montana case makes anything clear, it is that this court has dug in — no amount of unrestrained spending, no appearance of impropriety or actual corruption of our system is likely to dislodge this newly entrenched precedent from the threat it poses to our democracy. Regrettably, a constitutional amendment is required for that.

Fortunately, one of the nation's preeminent constitutional scholars, Harvard Law Professor Laurence H. Tribe, has drafted one, which I have introduced as H.J. Res. 111. It provides, simply, “Nothing in this Constitution shall be construed to forbid Congress or the states from imposing content-neutral limitations on private campaign contributions or independent political campaign expenditures.”

The proposed amendment also allows, but does not require, public financing of campaigns when states choose to enact such laws: “Nor shall this Constitution prevent Congress or the states from enacting systems of public campaign financing, including those designed to restrict the influence of private wealth by offsetting campaign spending or independent expenditures with increased public funding.”

The tidal wave of independent expenditures creates an unmistakable appearance of impropriety, and over time, it cannot help but corrupt. Independent expenditures, like direct contributions, should be subject to reasonable limits and should be transparent. And corporations are not people. For if they were, as Justice Stevens’ dissent points out, how could we deprive them of the right to vote?

ADAM SCHIFF (D-Burbank) represents the 29th Congressional District.