So while there was no entrance poll data in Colorado and while Mr. Romney may have been more organized in Nevada, we can still probably conclude that voter preferences have been incredibly fickle in this primary season. I don’t think you can develop a successful theory about this race unless you assume that voters are changing their minds — a lot. Some demographic groups may be more inclined to support certain candidates than others — but there are a lot of swing voters, and they have been swinging.

That unpredictability makes a case for betting on Mr. Santorum, who is given just a 13 percent chance of winning the Republican nomination on the betting market Intrade right now.

If the Republicans were neatly coloring in the demographic and geographic lines — as Mrs. Clinton and Mr. Obama did — then the small lead that Mr. Romney enjoys in the delegate count so far would be more definitive. The eight states that have voted so far are a reasonably representative sample, so if demographics are destiny, you might be able to make some precise-seeming projections going forward.

If the map is more scrambled, however, those predictions have a greater margin of error. There might be 15 or 20 states that lean toward Mr. Romney and 15 or 20 that lean against him, but few are truly safe calls.

Instead, Mr. Romney’s lead is more like the one held by a driver leading the Indianapolis 500 — after six laps have been completed.