You’ve probably heard by now that next week the Supreme Court will break up its summer recess to hear argument, for the second time, in Citizens United v. FEC. You may have the sense that this doesn’t happen often and that something important is going on. If so, you’re right and then some.

The case involves a film, Hillary: The Movie, that was produced by Citizens United, a conservative, non-profit corporation, to coincide with the 2008 presidential primary season. The case began as a fairly sleepy challenge to the Federal Election Commission’s (FEC’s) decision to treat the film’s production and release as corporate electioneering subject to campaign finance regulations, but was transformed by an order issued by the Supreme Court on June 29th. Here are five reasons why Citizens United is now a truly momentous case:

1. President Palin, Courtesy of Chevron: Let’s start with the biggest and most obvious reason this is a momentous case. Citizens United is arguing that expenditures by corporations in elections should be treated identically to those of individuals. If the Court accepts this argument, it would do away with a distinction that has been in place in our Constitution since the Founding and our statutory law since the Tillman Act of 1907 (as explained in the brief CAC filed in Citizens United), and allow corporations to spend unlimited amounts of money in elections. To appreciate how scary this change would be, consider that, according to the FEC, the Republican and Democratic parties combined spent slightly more than $1.5 billion between January 1, 2007, and December 31, 2008, while Fortune Magazine reports that the 10 most profitable companies during the same period earned combined profits of over $350 billion. This contrast reveals that unleashing even a tiny fraction of corporate profits – from just a handful of companies – could overwhelm the campaign system with money that represents the narrowest interests of private, profit-driven entities.

2. A Reargued Case in September is like a Snowstorm in July: This case is loaded with Supreme Court rarities, starting with the fact that the Supreme Court failed to decide this case the first time it was heard last Term. Also rare is that the Justices have decided to come back from summer vacation a month early for a pre-Term special session in order to rehear the case, and have specifically asked the parties to brief the question of whether they should overturn not one, but two prior rulings (Austin v. Michigan Chamber of Commerce, and the parts of McConnell v. FEC that uphold regulation of corporate spending in candidate elections). Ironically, the last time the Court interrupted its summer recess for a special session was to hear one of those cases, McConnell v. FEC, six years ago. Before McConnell, the Court hadn’t returned to DC for a pre-Term summer session since 1974, when in United States v. Nixon it ordered President Richard M. Nixon to surrender his secret Watergate tapes.

3. A Cast of a Thousand Stars (and a lawyer’s trick you should not try at home): Citizens United will be a scene of debut performances and veteran stars of the Supreme Court. It will be the first case to come before Justice Sonia Sotomayor and the first case argued before the Supreme Court by Obama’s Solicitor General Elena Kagan, who will argue on behalf of the FEC. The remaining line-up of participants in this case include the most experienced Supreme Court practitioners alive today – former G.W. Bush Solicitor General Ted Olson (representing Citizens United), former Clinton Solicitor General Seth Waxman (representing Sen. John McCain and other backers of the 2002 McCain-Feingold Bipartisan Campaign Reform Act, or BCRA) and preeminent First Amendment litigator Floyd Abrams (representing Sen. Mitch McConnell and others who opposed BCRA). Olson will be attempting the lawyer’s equivalent of a quadruple lutz: getting the Supreme Court to overrule case law he successfully convinced the justices to make just six years earlier. (As Solicitor General for President Bush, Olson defended BCRA in McConnell.)

4. The Alito Court: A lot of attention has focused in recent months on whether and how new Justice Sotomayor will change the Supreme Court. But oral arguments in Citizens United on September 9th should snap our focus back to a far more momentous change in the Court’s make-up: the 2006 replacement of Justice Sandra Day O’Connor with Justice Samuel Alito. It is only over time that we are seeing how significantly that change moved the Court’s center of gravity rightward. As in so many areas, Justice O’Connor emerged during her tenure as the Court’s critical swing vote in campaign finance cases and in McConnell in 2003 she provided the fifth vote necessary to uphold key portions of BCRA. In Citizens United, the Court has asked the parties to brief whether important parts of Justice O’Connor’s and Justice Stevens’ joint opinion for the Court in McConnell should be overruled.

5. The Roberts Court and Stare Decisis: In a 2007 campaign finance case, FEC v. Wisconsin Right to Life, Inc., the Court’s five conservatives mostly agreed on the merits, but clashed angrily about whether to overrule prior rulings of the Court including Austin and McConnell, with Chief Justice Roberts and Justice Alito joining together on the controlling opinion, which limits these cases without overruling them. This prompted Justice Scalia to unleash his famously acerbic pen on his new Chief, saying at one point that Roberts’s “faux judicial restraint is judicial obfuscation.” Citizens United will help answer a profoundly important question about whether there is in fact a meaningful difference of opinion among the conservative justices on the question of what justifies overturning prior rulings of the Supreme Court. The answer to this question will go a long way toward determining whether the Court’s shift to the right will be gradual or sharp in the coming years.