McCutcheon gives the Supreme Court under Chief Justice John Roberts an opportunity to halt its relentless march toward legalizing bribery in our politics and instead to re-affirm a self-evident truth: that big money contributions to candidates create an unacceptable risk of corruption.

No serious person questions the power of money in our politics. Whether in Washington, at the statehouse or at city hall, major donors get major access to the officials their money helps elect; their lobbyists are invited to help write and amend laws, and they are rewarded with government jobs and tax breaks.

All of this is legal, the court says, so long as there is what lawyers call ‘no quid pro quo corruption’ — no providing of a specific favor in exchange for a specific contribution.

That is more than bad enough, but Mr. McCutcheon and his lawyers want the court to make it worse by inviting the wealthy to put even more of their money into the system. At its core, their argument is that the right of free speech guaranteed by the Constitution is also a right to purchase political influence.

We yield to no one in our support for free speech. But the exercise of every freedom under the Constitution is subject to a balancing test. Slander and libel laws properly constrain freedom of speech and of the press. Freedom of assembly does not give demonstrators the right to indefinitely occupy public parks or private property. The right to keep and bear arms does not allow a citizen to purchase one of the Army’s howitzers or the Navy’s Tomahawk missiles.

In this case, the aggregate contribution limits now in place allow Mr. McCutcheon and other wealthy donors to spend more than enough money to make their views known to their representatives and their fellow citizens. The potential for corruption — indeed its inevitability — if those limits are removed is clear and present and more than sufficient to justify keeping them in place.