Republicans are voting today in primaries in Alabama and Mississippi, and they’ll caucus in Hawaii and American Samoa. What's at stake? 

As I said last week, we’re in the midst of a long slog to the nomination; if voting groups in upcoming states continue to do what those groups have done so far, Mitt Romney will clinch the nomination sometime in late May or June. However, another very real possibility is that at some point Republican Party actors start a stampede toward Romney, and the nomination wraps up very quickly as a result. I think that's the most likely outcome. There's also the possible, but extremely unlikely, scenario of a stampede to Rick Santorum.

So today's primaries? Sorry to disappoint, but I'll agree with the conventional wisdom: If Mitt Romney wins two states in the Deep South, that certainly could be the trigger for a stampede. If he wins one and finishes a close second in the other? I doubt it, at this point. If party leaders wanted to shut things down just because Romney is all-but-certain, presumably they would have done so already.

On the other hand, there's really nothing Rick Santorum can do to start a rush to him today. He can, perhaps, push Newt Gingrich out of the race by finishing ahead of the former speaker in both states, but that's about it, and it's not clear what incentives Gingrich is following anyway, so it's not clear what would get him out. 

In other words, this is probably the third chance — after South Carolina and Super Tuesday — that Mitt Romney has had to (possibly) end the active nomination fight with a very good night. But remember: The downside here isn't that the nomination will be at risk, only that he'll have to keep contesting primaries for at least a while longer.