A sharply-divided US Supreme Court engaged in a pointed debate on Tuesday over whether limiting the total amount of money an individual can give to federal candidates and political committees violates the free-speech rights of would-be campaign contributors.

By the conclusion of the hour-long argument it appeared the aggregate campaign finance limits under challenge would be struck down. But it also seemed likely that in accomplishing that result the majority justices would wield a scalpel rather than a meat ax.

At issue in the case, McCutcheon v. Federal Election Commission (12-536), is a provision of federal campaign finance law that restricts the total amount of money an individual can give during a two-year election cycle.

Those challenging the law complain that contributors are already subject to base contribution limits of $2,600 per candidate and up to $32,400 for political committees.

Those base limits were set by Congress to protect against the threat of excessively large and potentially corrupting contributions from one individual to a candidate or party.

The question in the case is whether given those base limits, the second-tier of regulations – the so-called aggregate limit set at $123,200 – is necessary and constitutionally justified.

The case stems from a lawsuit filed by Alabama businessman Shaun McCutcheon, who in 2012 gave contributions to 15 federal candidates and various committees. He wanted to give to 12 additional candidates and three national political committees, but those extra contributions would have put him over the aggregate limit even though each individual contribution would have complied with the base contribution limits.

He sued, claiming the law violated his free-speech right to contribute to candidates and causes within the base limits established by federal law.

The division among the justices on the case is sharp and clear. The court’s four-member liberal wing supports the aggregate limits as a necessary part of an overall system of campaign finance regulations.

In contrast, the court’s conservatives are concerned about the cost to free speech rights of the government limiting how much money contributors can give – even when they comply with base contribution limits that avoid an appearance of corruption.

US Solicitor General Donald Verrilli told the justices that if the aggregate limits were removed, candidates and party officials would be able to circumvent the remaining base limits and theoretically funnel up to $3.6 million from an individual into campaign funds.

“The very fact of delivering that check [for $3.6 million] creates the inherent opportunity for quid pro quo corruption,” Mr. Verrilli said.

Chief Justice John Roberts brushed aside the threat of possible circumvention, and sought to turn the argument instead to the free speech cost to contributors of having to comply with both base and aggregate limits.

“The aggregate limit would have the effect of restricting the ability of a contributor to make the maximum contribution to more than a certain number of candidates,” Verrilli conceded. “We can’t help but acknowledge that. It’s math.”

The solicitor general added that contributors who wanted to give more to support political candidates and causes could spend unlimited amounts of money through super PACs.

That suggestion was somewhat ironic given the Obama administration’s fierce opposition to the Supreme Court’s 2010 decision in the Citizens United case, which held that the government could not limit the amount of money being spent by corporations and unions in independent political advertisements.

Justice Antonin Scalia recognized the apparent inconsistency. Many campaign reform advocates – including the Obama administration – support efforts to limit the amount of “big money” contributions in the political system.

“If gratitude is corruption, you know, don’t those independent expenditures evoke gratitude,” Justice Scalia asked.

Verrilli responded that despite the court’s earlier ruling allowing unlimited independent expenditures, federal law continues to restrict contributions to political candidates and parties. Without aggregate limits, there would be a risk of circumvention of large enough amounts of money to pose an inherent risk of corruption, he said.

Justices Elena Kagan and Stephen Breyer repeatedly expressed concern about the possibility of circumvention of campaign finance laws if the aggregate limits are struck down.

In contrast, Justice Samuel Alito dismissed the suggestion as “wild hypotheticals that are not obviously plausible or certainly lack any empirical support.”

Later in the argument, Chief Justice Roberts returned to his earlier question. He said he appreciated Verrilli’s argument about possible funneling of $3 million and that aggregate limits prevent it. “But what do you do about the flip side,” Roberts asked. “I mean, you can’t pretend that this is pursued with no First Amendment cost.”

Roberts said the aggregate limits impose “a very direct restriction on much smaller contributions that Congress said do not present a problem with corruption.”

Verrilli responded that the aggregate limits were similar to a rule that prevents federal officials from receiving gifts like an expensive sports car. It is an entirely content-neutral justification for a rule that helps protect against corruption, he said.

“That normally doesn’t get you very far on the First Amendment,” Roberts responded. “You could not have a rule that says the [Washington] Post or the New York Times can only endorse nine candidates.”

Verrilli conceded that the aggregate limits impose costs to free speech rights. But he said the costs were mitigated because the contributor was free to donate to as many candidates as he/she wanted and was only limited in the amount of the contributions.

The chief justice then asked Verrilli if there was any middle ground that would address his circumvention concerns without imposing First Amendment costs on would-be campaign contributors.

The solicitor general responded that the aggregate limit could be raised to a higher level by Congress. But he added that those challenging the law are asking that it be struck down entirely.

“We think the risk of corruption is real,” Verrilli said. “And we think it’s in fact profound when you are talking about the kinds of [multi-million dollar] contributions that can be made if you take the lid off on aggregate contributions.”