Their exchanges defined a substance-heavy event, and both candidates held their ground. In a debate focused on global turmoil fueled by the rise of ISIS, those dominating performances by relative newcomers could help both candidates clear a commander-in-chief test in the minds of primary voters. And they will arguably advance each in his case that he’ll be one of the last standing in a still-sprawling GOP field.

But there were other standout turns at the Venetian Hotel & Casino in Las Vegas. Former Florida Gov. Jeb Bush, clinging to viability as he fades in the polls, brought a sharp critique to current frontrunner Donald Trump, a man who deposed him atop the field in early summer and seemed to rattle him in the first debates. Bush called Trump a “chaos candidate” who’d be similarly disastrous in office. “Donald, you’re not going to be able to insult your way to the presidency,” he said during one their several clashes, to big applause. “That’s not going to happen.”

Trump himself, now soaring in national surveys after his controversial proposal to ban Muslims from entering the country, appeared mostly serene at centerstage. Trump did restate his recent calls for “closing” parts of the Internet to limit terrorists ability to access it and killing the family members of known terrorists — positions that Kentucky Sen. Rand Paul pointed out, respectively, would violate the First Amendment and the Geneva Conventions. And Trump later flubbed a question on the nuclear triad, answering in a manner that indicated he was entirely unfamiliar with the concept. But since Trump’s outrages only seem to goose his standing, it’d be tough to argue that anything he said Tuesday night would undercut the support he’s amassed.

Likewise, more broadly, with seven weeks until voting kicks off in Iowa, it’s not clear that the fifth and final Republican debate of the year will change the trajectory of the race.

None of the candidates on the stage who needed a game-changing performance to earn a plausible path to the nomination managed to pull that off. Retired neurosurgeon Ben Carson, for example, has been steadily slipping since the attacks in Paris and San Bernardino elevated terrorism as a top voter concern. And while Carson evidently studied for this event to demonstrate he can speak knowledgeably about foreign policy, he also complained mid-event about his lack of airtime and acknowledged in an interview with debate host CNN afterward that the terrorist attacks had cost him. Neither did Sen. Paul or former Hewlett-Packard CEO Carly Fiorina, both of whom fought their way into the conversation at times, appear to do enough to earn the second looks they need.

One of the night’s most anticipated confrontations — between Trump and Cruz, now an arm’s length away in the middle of the stage, thanks to his Iowa surge — failed to materialize. Leaked recordings from a recent Cruz fundraiser revealed the Texas Senator questioning Trump’s judgement and qualifications to be president and talking up his own strategic play to embrace Trump publicly in hopes of inheriting the billionaire’s supporters once he falters. Trump since has blasted back, calling Cruz a “maniac” whose habit of antagonizing friend and foe alike in the Senate would hobble his ability to get anything done from the Oval Office.

Asked to articulate those criticisms in person, both demurred. Trump said he’d “gotten to know [Cruz] over the last three or four days. He has a wonderful temperament.” And Cruz responded in kind, backing off the ad hominem sting with a generic statement that “the judgment that every voter is making of every one of us up here is who has the experience, who has the vision, who has the judgment to be commander in chief. That is the most important decision for the voters to make.”

Instead, the event’s hallmark fight pit Rubio against Cruz on fundamental questions about the right approach for the U.S. in confronting ISIS amid the violent muddle in the Middle East. Rubio hewed to a more hawkish position, calling for major investments in rebuilding American defense capabilities and the toppling of Bashar al-Assad’s regime in Syria. He laced into Cruz’s voting record, arguing the Senator has undercut intelligence gathering and military strength. Cruz defended those votes as striking a necessary balance with protecting civil liberties. And he argued recent history has shown taking out Middle Eastern strongmen, as distasteful as they may be, sows discord the U.S. can’t contain while creating vacuums that terrorist organizations are happy to fill.

That’s as close to a basic philosophical divide as exists in the field, and all the candidates on the stage fall on one side or the other. But it was most vividly joined in the back-and-forth between Rubio and Cruz. The two also clashed over immigration. There, Cruz stayed on the attack, repeatedly accusing Rubio of aligning with liberalizers like Sen. Chuck Schumer (D-N.Y.) in his 2013 bid for a bipartisan immigration reform package. And Cruz conflated the issue with the night’s organizing topic, arguing that “the front line with ISIS isn’t just in Iraq and Syria, it’s in Kennedy Airport and the Rio Grande. Border security is national security.”

Rubio, in a rare defensive posture, explained he’s evolved toward a harder-line position on immigration because he learned the American people aren’t ready for the approach he advocated two years ago. Further, he suggested the world has changed, with GOP voters newly sensitized to a threat they perceive from Syrian refugees. But Cruz recognized correctly that Rubio’s history on the issue remains a major vulnerability for him with the conservative base, one that hasn’t been fully exploited yet by his rivals.

Trump created some news by once again foreswearing an independent bid — an option he appeared to abandon when he signed a loyalty pledge to the Republican Party back in September only to publicly flirt with the possibility again in recent weeks. But given his demonstrated flakiness toward the commitment, it’s easy to imagine Trump reviving the specter of bolting if his support within the GOP starts to flag.