In a much-anticipated decision on Thursday, the Supreme Court virtually gutted an important section of campaign finance law that prohibited corporate spending in elections.

Politicians, campaign finance lawyers and politicos had been waiting for the Citizens United v. Federal Election Commission decision since it was reargued before the Court in early October with either great anticipation or great fear – depending on what side of the issue they were on. In a five-to-four decision on Thursday, the Court said the government cannot restrict corporate and union spending on ads and other election communications that expressly advocate for the election or defeat of a candidate in the days leading up to an election.

The case, as we have written before, involved Citizens United, a conservative nonprofit corporation that sought to air a documentary titled, "Hillary: The Movie" on a video on demand service in the 30 days leading up to the 2008 presidential primary. The Federal Election Commission intervened, saying the film amounted to a political communication and thus, could not be aired at that time.

The Court issued a broad decision and ruled on the constitutionality of one section of the law, seemingly without being asked to do so by Citizens United. In so doing, the court overturned its 1990 holding in Austin v. Michigan Chamber of Commerce that held both that political speech may be banned based on the identity of the speaker and that corporate expenditures have "distorting and corrosive effects" on elections.

If the Court chose to rule narrowly, it could have considered only whether the video on demand service should be regulated under the Bipartisan Campaign Reform Act of 2002 (or McCain-Feingold), or whether Citizens United was the type of group that McCain-Feingold was meant to regulate.

The Supreme Court called a special session on Thursday to announce the decision – something that is very rare. Justice Anthony Kennedy wrote the majority opinion, which was supported by Chief Justice John Roberts and Justices Samuel Alito, Antonin Scalia and Clarence Thomas. Kennedy, who was expected to be the swing vote in the case, said on Thursday that "if the First Amendment has any force, it prohibits Congress from fining or jailing citizens, or associations of citizens, for simply engaging in political speech." He went on to say that Austin interferes with the market place of ideas. "It uses censorship to control thought," Kennedy said. Kennedy added that "without Austin, the government cannot limit corporate independent expenditures."

The scene at the Supreme Court for the decision was far different than it was when the court heard rearguments in October. There were far fewer people in the audience and less reporters in the press box. In October, several lawmakers were in attendance, namely campaign finance reform champions Sens. John McCain (R-Ariz.) and Russell Feingold (D-Wisc.). On Thursday, I could only see Senate Minority Leader Mitch McConnell (R-Ky.) – who challenged McCain-Feingold in a 2003 Supreme Court case – and Florida freshman Rep. Alan Grayson (D).

In the front row, David Bossie, the president of Citizens United, sat anxiously. He remarked to his small cadre that he hadn't slept well the night before and eagerly greeted McConnell when the senator arrived. He sat motionless as Kennedy delivered his remarks. Afterward, he called the ruling "monumental" and said that he was "extremely grateful and humbled."

The bulk of the remarks while the court was in session, though, were delivered by Justice John Paul Stevens. Stevens wrote the 90-page dissenting opinion, with which Justices Ruth Bader, Stephen Breyer and Sonia Sotomayor concurred. Stevens, his voice cracking at times, tore into the majority opinion, saying he "emphatically disagrees" with it. In particular, he chastised the majority for taking up the constitutionality of the section of McCain-Feingold when it wasn't asked to. He then ticked off a litany of "errors" in the majority opinion.

These included questioning the majority's recollection of history. Stevens said the government – and the Supreme Court – has repeatedly said that it can limit the right to free speech depending on the identity of the speaker, in this case corporations. Further, he scolded the majority for granting free speech protection to corporations. "Corporations are not human beings," he said. "The ruling announced today represents a radical change in the law."

Afterward, Floyd Abrams, perhaps the preeminent First Amendment lawyer in the country who argued aspects of the case, summed up reach of the Court’s ruling in one word: "Far."

"It was a sweeping decision that made it very clear that the First Amendment protects corporate speech about politics and government," he said. "It is not for Congress to decide who can say what. It is a holding that corporate expenditures are protected by the First Amendment just as independent expenditures are protected by the First Amendment."

In many ways, the breadth of the decision caps off a trend in campaign finance law. As I wrote in our January issue, over the past few years courts have been chipping away at McCain-Feingold and its intent. This ruling is more than just another flesh wound, however, it is a gutting of one of the principles of the law.

Abrams also made the point, though, that this may be more of an ideological victory that may not have huge practical effects. In about half of the country's states, unlimited corporate expenditures are already permitted and there isn't much of a difference in corporate spending in those states compared to others.

Abrams' remarks raises the question of just what impact this will have on the 2010 and 2012 elections. It is very hard to say at this point. What is clear, though, is that the airwaves in 2010 and 2012 could, as a result of this decision, look quite different.

Jeremy P. Jacobs is the staff writer for Politics magazine.