Shaun McCutcheon, electrical engineer and self-described “conservative with a pretty good libertarian streak,” remembers the first time he was shown a “massively confusing chart” about federal limits on political contributions.

No more than $48,600 to candidates for federal office per two-year election cycle. No more than $74,600 to political parties and political action committees. Maximum $123,200 total.

The Alabama Republican didn’t understand why he couldn’t write as many checks as he wanted, and he asked a Republican lawyer friend. “He said, ‘Oh, you can challenge those. It will go all the way to the Supreme Court,’ ” McCutcheon told me. “I didn’t believe it would actually happen.”

On Tuesday morning, McCutcheon will be at the court for oral argument in McCutcheon v. Federal Election Commission. Campaign finance reform advocates warn the case could be the next Citizens United, further dismantling limits on big money in politics. Opponents hope they’re right.

In a world of $10 million checks to super PACs, the notion of strict overall limits on giving directly to candidates and parties has a rather quaint ring. In the aftermath of Citizens United and related cases, donors interested in pumping big money into elections have ample opportunities. Donors seeking to steer mega-resources to a campaign aren’t especially constrained by the $2,600 limit on direct giving to a particular candidate.

Is a candidate aware of a donor’s big check to a supposedly independent super PAC really less indebted than if the contributions went directly to candidates and parties, violating the limits at issue in McCutcheon?

Still, lifting the limits on overall direct giving would further undermine a system awash in big money. After all, it was only 11 years ago that Congress banned unlimited “soft money” contributions to political parties. With election lawyers adept at setting up joint fundraising committees that collect cash for multiple candidates simultaneously, eliminating overall limits would reopen the soft money spigot for individual donors.

In addition, dollars that flow directly to candidates are more valuable to them — candidates get to control the message and spending — and therefore potentially more corrupting. And even in an era of super PACs, it’s chilling to imagine individuals being legally allowed to funnel — and, worse, office holders or candidates being legally allowed to solicit — direct contributions totaling more than $3.6 million (the sum if someone gave the maximum to all Senate and House candidates and party committees).

But the stakes in McCutcheon’s case don’t simply involve the precise limits themselves. What matters for the future of campaign finance rules, should the justices rule for McCutcheon, is what rationale they use.

Since the 1976 decision in Buckley v. Valeo, the court has distinguished between limits on campaign contributions and limits on political spending. Contribution limits are treated with deference, and have almost always been upheld, on the theory that they prevent corruption or the appearance of corruption while imposing a “marginal” restriction on speech. What matters, the court has said, is the symbolic act of contributing, not the size of the check. By contrast, restrictions on spending are subject to the toughest test because they directly curtail individuals’ own speech and, at least in the court’s dubious view, such independent expenditures by definition can’t be corrupting.

Time was that advocates of limits on campaign cash lamented the contribution/expenditure distinction because it was used to strike down spending limits. Now they cling to it as the last bulwark against a campaign finance free-for-all.

McCutcheon’s lawyers, the Republican National Committee and Senate Minority leader Mitch McConnell have asked the court to use his case to overrule Buckley and subject both contribution and spending restrictions to strict scrutiny as intrusions on free speech.

Three justices — Antonin Scalia, Anthony Kennedy and Clarence Thomas — are on record calling for Buckley to be overruled. Chief Justice John Roberts and Justice Samuel Alito have resisted that urge, and the court could invalidate the overall contribution limits without going so far. Yet the activist inclination displayed in Citizens United could re-emerge. The court granted separate time to the lawyer for McConnell, whose brief focuses on overruling Buckley, to argue for that outcome.

The consequences, as the Campaign Legal Center has warned, “would destabilize all contribution limits.” Already the RNC’s lawyer, James Bopp, has cases in the pipeline attacking the long-standing ban on corporations donating directly to candidates. Limits on individual’s contributions to particular candidates might survive even under a stricter standard, but a challenge would certainly be mounted.

This is a case to watch — and a cause for worry.

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