In an opinion declaring that the Supreme Court must “give the benefit of the doubt to speech, not censorship,” Chief Justice Roberts handed down a decision yesterday that all but repeals Congress’s 2002 ban on so-called sham issue advertising on television and radio in the days before federal elections.

The ruling holds the potential to shake up the 2008 presidential race by opening the door to unions, corporations, and nonprofit groups that had been shut out of the political process by the Bipartisan Campaign Reform Act of 2002, better known as McCain-Feingold, which banned broadcast advertisements naming a candidate for federal office in the 30 days before a primary election and the 60 days before a general election. But lingering uncertainty over the new legal regime may prevent many groups from immediately jumping into the fray.

Writing for a 5–4 majority — which included Justice Alito in whole and Justices Scalia, Thomas, and Kennedy in part — Justice Roberts said that a Wisconsin anti-abortion group should have been allowed to air ads drawing attention to Senator Feingold’s opposition to some of President Bush’s judicial nominees ahead of the 2004 election. He further argued that the Federal Election Commission’s test for determining which ads are legitimate issue ads and which are merely campaign ads in disguise was too broad, writing that “the First Amendment requires us to err on the side of protecting political speech rather than suppressing it.”

The disagreement in the majority came over the question of whether the case called for a new, less-restrictive test of an ad’s legality or whether the ad ban should be overturned in its entirety. Justices Scalia, Thomas, and Kennedy argued in concurring opinions for overturning the ad ban. Justices Roberts and Alito said the case before them did not require such a far-reaching decision — though Justice Alito’s one-page concurrence seemed to invite a future case that would offer the opportunity to revisit the question.

The single dissenting opinion — penned by Justice Souter and joined by Justices Stevens, Ginsburg, and Breyer — argued that the majority’s opinion flew in the face of Congress’s will and would breed “pervasive public cynicism” about the American political system.

Proponents of campaign-finance regulation immediately criticized the court’s decision, predicting that corporate and union money would start flowing into the 2008 election.

“With today’s decision, the court has opened the door again for corporations and unions to evade this critical anti-corruption statutory provision,” the president of the pro-regulation group Democracy 21, Fred Wertheimer, said in a statement.

Supporters of campaign-finance deregulation, however, argued that the vagueness of the ruling — banning only ads that “no reasonable interpretation” could find to be true issue ads — would prevent many groups from rushing in.

“What’s unclear is the scope of the advertising that might be permitted,” said an attorney for the Chamber of Commerce, Jan Baran. “The test that the Supreme Court opinion provides is a little vague.”

Groups looking to run ads, either in the primaries or the general election, now have essentially three options: to seek a declaratory judgment from a district court that their ads are acceptable, to seek an advisory opinion from the FEC as to their ads’ acceptability, or to simply go ahead with their ads and risk running afoul of the law.

“I think there will be a little more caution than some of the regulators think,” a former FEC commissioner and outspoken critic of campaign-finance regulation, Bradley Smith, said.

“Your first stop is your election lawyer,” a scholar at the libertarian Cato Institute, John Samples, said. “I don’t think you could get a decision in time for the primaries … My sense is it would take a year or two, not for the next election.”

However, if there’s one thing that supporters and opponents of yesterday’s decision agreed on, it’s that the Roberts court is far less amenable to attempts to curb the influence of money in politics that the court that upheld the bulk of McCain-Feingold in 2003, in a decision known as McConnell v. FEC.

“The tone is one of deep skepticism for campaign finance regulation,” a professor at Loyola Law School, Rick Hasen, said. He called the new tone a “sea change.”

“I think Chief Justice Roberts is a very smart man,” Mr. Hasen said. “And what he’s doing is gutting McCain-Feingold.”

Senator McCain, who is a Republican presidential candidate, yesterday greeted the decision with a statement saying, “While I respect their decision in this matter, it is regrettable that a split Supreme Court has carved out a narrow exception by which some corporate and labor expenditures can be used to target a federal candidate in the days and weeks before an election.”

He said the court’s decision “does not affect the principal provision of the Bipartisan Campaign Reform Act, which bans federal officeholders from soliciting soft money contributions for their parties to spend on their campaigns.”

Mitt Romney, a rival presidential candidate, issued a statement saying the decision showed that McCain-Feingold was “a poorly-crafted bill” that “trampled the basic right of the American people to participate in their democracy.”

Mayor Giuliani, a longtime supporter of McCain-Feingold, called the decision “a welcome victory for free speech and personal liberty. … The ruling protects freedom to participate in the electoral process and recognizes political free speech is the foundation of our First Amendment rights.”