The undisputed Republican frontrunner on Tuesday privately signed and then publicly presented a “loyalty pledge” that commits him to backing the GOP presidential nominee, even if that’s somebody else. More significantly, the contract binds Trump from launching an independent bid should his pursuit of the Republican nod fall short.

“I have signed the pledge,” Trump told a capacity crowd of media and onlookers at his Trump Tower in midtown Manhattan. He then held up the signed document and added he “will be totally pledging my allegiance to the Republican party and the conservative principles for which it stands.” Trump appeared before the cameras after concluding a closed-door tete-a-tete with Reince Preibus, the Republican National Committee chairman, who’d traveled to New York for the purpose.

The decision marks an about-face for Trump, who opened the first Republican presidential debate last month by refusing an invitation from the Fox News moderators to rule out a third-party run. “I’m talking about a lot of leverage,” he said at the time, meaning that the threat he could bolt would keep Republican party bosses in hock to him rather than the other way around.

Explaining what’s changed in less than a month since, Trump on Tuesday pointed to his position in the polls. The latest, a Monmouth University survey released Thursday, showed him reaching a record-high 30% support nationally, a 7% increase over his position in the same poll when it was conducted before the Republican debate.

Trump said he hadn’t redeemed his “leverage” for anything in return for his pledge —except a guarantee from Preibus that the official party apparatus will continue to treat him fairly. Arguably, Trump didn’t sacrifice much by signing, since mounting an independent run would prove an expensive and organizationally vexing challenge at this point. And it’s hardly clear what power the RNC has to enforce the document if Trump decided he wanted to anyway.

On the flip side, by affirming his loyalty, Trump inoculates himself — to a degree — from the attack that he’s nothing more than an opportunist using the party to promote himself. That critique has been voiced most loudly by former Florida Gov. Jeb Bush, and the former frontrunner showed Thursday afternoon he won’t be abandoning it. He tweeted his own version of the pledge, making clear his voting record has been ruby-red since 1972, an thinly-veiled shot at Trump’s liberal past.

.@realDonaldTrump pic.twitter.com/RbagyBXspr

— Jeb Bush (@JebBush) September 3, 2015

But partisan fealty is not the same thing as ideological conformity — a fact that Trump’s improbably enduring lead is demonstrating in realtime. That Trump has now at least nominally removed any doubt about his Republican allegiance will do nothing to quell a much more consequential debate his rise has touched off within the party about what it means to be a conservative.

Before Trump stepped on the scene, there was a rough consensus among party elites that the appellation demanded a commitment to lower taxes, free trade, trimmed entitlement benefits, and a path to citizenship for immigrants already within our borders. Trump is shredding the consensus, rejecting each of its pillars and nevertheless (or, perhaps, as a result) building wide, deep support among the party’s base. For that reason, Trump’s move today could be just as menacing to the party’s establishment — tantamount to the scene in the horror movie when the intruder locks himself inside the house. His popularity will continue to force the field to reckon with his positions. And when his rivals call out his conservative apostasies, Trump can now borrow a line from Ohio Gov. John Kasich, a fellow contender for the nomination who’s at times likewise proved idiosyncratic in his approach to policy. As Kasich is fond of saying, “The Republican party is my vehicle and not my master.”