There are exceptions, of course: The candidate who attracts the most support in the invisible primary doesn’t always win. That’s especially true for candidates who attract a plurality but not a clear majority of support in the invisible primary, like Mrs. Clinton in 2008. In these instances — when the party doesn’t make a clear decision — it becomes easier for another candidate to win the nomination, although the winning candidate almost always has won significant support in the invisible primary.

Mr. Bush’s pre-emptive efforts have the potential to be extremely consequential. He could secure enough support to dissuade other potential candidates, like Marco Rubio or Mitt Romney, from running (although Mr. Romney surprised some on Friday by reportedly saying that he was considering entering the race). Mr. Bush could also deal a big blow to the fortunes of candidates with a tougher road to the nomination, like Chris Christie or Rick Perry, who might have otherwise counted on some of Mr. Bush’s supporters.

In the best case for Mr. Bush, he could conceivably secure enough support to become the clear front-runner in a nomination fight that many analysts have long assumed would be wide open. Even short of that best case, Mr. Bush’s early aggressiveness is probably damaging to the prospects of Mr. Christie, Mr. Rubio and Mr. Romney.

There’s a bit of a debate about the extent to which the invisible primary actually matters or merely reflects other factors that matter — that is, whether it is causal or correlative. Does the winner of the invisible primary win the nomination because of the benefits that come from being its victor? Or because the winner of the invisible primary tends to be the best candidate, who therefore might be expected to win the primaries anyway? My view is that it’s causal, a view that is most completely articulated in “The Party Decides,” a book by four political scientists: Marty Cohen, David Karol, Hans Noel and John Zaller.

The book has been misread in some circles as evidence that the moderate wing of the Republican Party has an advantage in the Republican nomination process. Although I think the relatively moderate wing does have an advantage (I’ll talk about that more in coming weeks), I don’t think it’s mainly because of the invisible primary.