The U.S. Supreme Court will hear Christian Legal Society v Martinez, 08-1371, on April 19. This is not an election law case, but it is a freedom of association case, so it will likely impact the law on political parties. The issue is whether a public law school can require student groups to admit any student (at that school) as a member.
The amici briefs are all in now, and they are overwhelmingly against the law school. There are 22 amici briefs on the side of the Christian Legal Society, and none on the side of the school. There is also one brief in support of neither side. To see these briefs, use this American Bar Association web page link.