McCain was able to win narrow pluralities in early primary states courtesy of the votes of non-Republicans in the Republican primaries. The Democrats have recognized the problem with such 'raidable' primaries, the Republicans should wake up to the problems, and close the primaries.
I understand they are working on [this] but, due to a number of conflicting court decisions, which is strange considering the ruling in California Democratic Party v. Jones, 530 U.S. 567 (2000), closing primaries may not occur until a subsequent election.
I fail to see the relevance of
California Democratic Party v. Jones. The issue of open primaries is not relevant to that case and Scalia's footnotes in his opinion indicate that he would at least give consideration to the idea that voting in an open primary is an act of association, and might even be in favor of that view. In any case, the closed primary is for now at least, impossible to implement in at least one early primary State, South Carolina. We have no party registration that could be used to close a primary.