California is likely to lose. It collected donor information for law enforcement purposes but allowed the information to leak. Even the liberal Justices Kagan and Sotomayor seemed concerned about this, and will likely either vote that AFP wins its “as applied” challenge or will vote to remand the case to reconsider the as applied challenge.
But the question of where the Court’s conservative supermajority is likely to go in this case is the important one. The Court could apply strict scrutiny in this case and strike down the law facially (applied to everyone, not just to the plaintiffs), which would lead not only to California losing but calling into question the constitutionality of all campaign finance disclosure laws.
That result seems unlikely, as I believe only Justice Thomas (and perhaps Alito and Gorsuch) will be willing to go that far. But that’s mostly about appearances. It could well be that the other conservatives (Roberts, Barrett, and Kavanaugh) will say they are applying the mid-level “exacting scrutiny” and strike down the law facially. They could well pull the same stunt Roberts pulled in McCutcheon, redefining exacting scrutiny so it looks much more like strict scrutiny. That will lead to more campaign finance disclosure laws being struck down by the Court’s but without a dramatic, Citizens United-type blockbuster holding. It’s Roberts’ style, and we could well see it here.
People paint conservatives with a single brush, but that’s wrong. Justices Scalia and Kennedy were staunch conservatives on key issues, but understood the public value of disclosure in preventing corruption, providing valuable information to voters, and helping enforce other laws like the ban on foreign contributions in elections. They knew that people spending large money in elections did not face great dangers of harassment (and are entitled to a campaign disclosure exemption if they could), and that this is about trying to avoid accountability for influencing the political process. A system that allows unlimited spending without disclosure does not represent the “Home of the Brave,” as Justice Scalia said.
I expect a decision by the end of June.