The law allowed candidates who qualified for public financing to receive a lump sum grant from the government if they refused to accept private contributions. It also allowed participating candidates to qualify for additional matching government funds if their opponents who chose not to participate in public funding spent more than the initial grant.
In its opinion, the majority targeted the so-called "trigger mechanism," which aimed to direct more public money to qualified candidates, and found that it violated the free speech rights of nonparticipating candidates.
Chief Justice John Roberts, writing for himself and the four other conservatives on the bench, stated that the matching funds provision "substantially burdens the speech of privately financed candidates and independent expenditure groups without serving a compelling state interest."
He said that laws "like Arizona's matching funds provision that inhibit robust and wide-open political debate without sufficient justification cannot stand."
In other words, evening up the playing field between privately funded campaigns and publicly funded ones is a violation of the first amendment rights of the privately-funded candidate, that inhibits their right to use money as free speech.
If that seems counter-intuitive and even downright fishy, it's because it is: it's the same argument used in Citizens United, that any government limits on private campaign money use is an inhibition of free speech. Yes, the first amendment absolutely exists to protect free speech from government interference, but this ruling basically says that not only is campaign money equivalent to free speech to the point it garners first amendment protections from the government regulation of it, but that only private campaign money gets this protection.
Chief Justice Roberts completely threw out the argument that the candidate who didn't have the resources was at the disadvantage, rather the candidate with the far greater amount of private money donations was in fact the one needing the protection.
Taking this argument to its endpoint is a rather frightening exercise. Those who have money have more free speech rights than those who don't, and they have every right to exercise its use as they see fit in order to influence political contests. The ruling leaves public financing of campaigns intact...for now. But I'd have to say that we can't be far away from the day where a publicly financed candidate who wins an election is sued over this by their privately funded opponent, claiming that public campaign funding of any type is unconstitutional.
When that happens, the corporations really will own the country.
[UPDATE] In completely non-related news, I'm guest blogging for DougJ this week over at Balloon Juice. Do behave yourselves over there.