The white (non-Hispanic) Catholic electorate is split right now on the presidential election:
Just after the party conventions, McCain was ahead with this group. Pollsters pay attention to this group as a group because it appears volatile. But it isn't, really. What this change means is that "Catholic" is not a voting bloc any more. The very fact that they have to report Anglo and Hispanic Catholics separately shows the cracks in Catholic as a political identity.
What they should show is liberal/progressive Catholics vs. conservative/traditional Catholics. I expect the former would go strongly for Obama, and the latter for McCain. The closest comparison we do have for traditional Catholics are evangelical Protestants, who go three-to-one for McCain.
I believe the election of John Kennedy normalized Catholics in politics at all levels. As a result, Catholics are no longer an electoral bloc, but are divided by ideological and economic issues, just as Protestants are.
I believe the election of Barack Obama will eventually have a similar effect for African Americans. Right now, the black vote is overwhelmingly Democratic. In fact, black Americans support the Democratic presidential candidates at higher rates than all registered Democrats do. In this election, not surprisingly, the black vote for Obama is likely to be above 90%, and black turnout will probably be the highest ever.
Twenty years from now, though, the black vote may be more divided between the parties. African American voters are likely to vote their ideology and economic interests. There will be more black Republican candidates, probably small government, anti-affirmative action, pro-life evangelicals. I pick twenty years because that is how long it took the Kennedy Catholic bloc to split into progressive Catholic Democrats and Reagan Democrats.
The Catholic bloc is no longer a bloc. Perhaps twenty years from now President Obama will mean that, ironically, the black bloc is no longer a bloc, either.