THE most important question of the moment, as the Republican Party prepares for the first of 1,162 or so presidential primary debates, isn’t really what Donald Trump will say or do on stage.

O.K., that might be the most immediately interesting question, and the best reason for people who aren’t professionally required to watch every single G.O.P. debate to tune in on Thursday night.

But what matters most, politically, about the “I Am Trump” spectacle isn’t what the Donald does but whom he helps. Trump won’t be the Republican nominee, but the eventual nominee may end up owing him a debt of gratitude for services rendered along the way.

For now, it’s easiest to see who will owe Trump their resentment, since just about every dark-horse candidate has been effectively bigfooted by the Donald. His rise has knocked past limelighters like Rand Paul and Ben Carson and Mike Huckabee downward in the polls, and put a comb-over-shaped lid on the hopes of Chris Christie, Bobby Jindal, Rick Santorum and Carly Fiorina. (When George Pataki writes his campaign trail memoir, “I Could Have Been a Contender,” it will mostly consist of complaints about how the wrong six-foot-plus New Yorker got all the media attention in the summer of ‘15.)

But among Trump’s potential beneficiaries, the man most likely to be indebted is Jeb Bush. A few months ago, Jeb looked like the weakest of front-runners: The field was deep, his own poll numbers were lackluster, and he was facing two candidates in particular – Marco Rubio and Scott Walker – who seemed just as capable of uniting the party, more appealing to the average Republican voter, and more compelling as general election candidates than another Bush dynast.

Walker and Rubio are still there, and Jeb’s weaknesses remain. But Trump has come bearing the former Florida governor several gifts.

First, his sudden prominence sets up exactly the kind of stylistic contrast that Jeb needed: He and the Donald are now the two most famous names in the race, they’re occupying opposing poles (populist/establishment, raffish/respectable) in a way that makes Jeb look like the safest harbor for anyone freaked out by Trump’s success, and the longer Trump polls well the less attention (and, perhaps, fund-raising dollars) there will be for more plausible challengers.

At the same time, Trump’s deliberately-outrageous shtick, his camera-hogging instincts, are providing cover for Jeb to run the kind of primary campaign he clearly wants to run – conceding a human role in climate change here, doing minority outreach there – without having controversy dogging his every centrist foray.

Given his name recognition and fund-raising base, Jeb doesn’t need the media spotlight right now, and there was a real danger — visible in his fumbling answer to questions about Iraq — that he would become a punching bag for the entire field across the early debates. Now that seems less likely, because everyone is scrambling to figure out how to handle Trump instead.

Third, Trump has thrust the immigration issue back onto center stage. On the surface, that seems like it might be bad news for Jeb, but his immigration heresies are probably baked into his brand; he’s winning on those terms or not at all. So having the issue front and center arguably creates more headaches for Rubio, who has been trying to tap-dance around his own comprehensive bill while he runs a little distance to Jeb’s right.

And having immigration front and center on Trump’s deliberately outrageous terms also creates difficulties for anyone who wants to take a kind of moderate-restrictionist position, as Walker has sometimes tried to do, because (so long as his polls hold) it will be Trump who gets to define who’s actually tough on illegal immigration and who isn’t.

Finally, Trump’s prominence may eventually give Jeb a rare chance to actually attack a rival from the right – since the Donald’s relatively-liberal past provides plenty of ripe targets. One of Bush’s challenges, facing Rubio or Walker or anyone else in the pre-Trump field, was figuring out a way to draw contrasts that would highlight his own pretty-conservative record. Now the opportunity is there.

Which doesn’t mean that he’ll seize it, or that his non-Trump rivals will flail and fold. Walker’s numbers have held up pretty well amid the Trump surge, Rubio’s fundamentals are still strong, there’s plenty of time for someone else to emerge from the pack … and Jeb is, after all, trailing in national polling at the moment, which is hardly the strongest place for a notional front-runner to be.

But Jeb wasn’t strong a few months ago either; he was always going to need more luck than his brother did in 2000 or Romney did in 2012. And having Trump on the stage this Thursday is the first major sign that he might get it — that fortune, always partial to dynasties, favors the Bushes yet again.