Sen. Marco Rubio takes part in the presidential debates at the Reagan Library in Simi Valley, California on Sept. 16. Justin Sullivan AFP/Getty

National security divided the 11 Republican candidates into two camps during Wednesday night’s debate: those who looked like future commanders in chief and those who looked unready for prime time.

Sen. Marco Rubio of Florida, despite limited speaking time, made the most of it with a thorough response on dealing with a newly aggressive Russia and an explanation of why he hesitated to support American force in Syria. New Jersey Gov. Chris Christie reminded viewers about his prosecution of terror cases as a former U.S. attorney. Sen. Ted Cruz of Texas delivered a meticulous indictment of the Iran deal. Carly Fiorina, in a strong overall debate performance, demonstrated a detail-oriented facility talking about foreign policy. And Jeb Bush delivered the line of the night in embracing his brother’s record of preventing a terrorist attack on U.S. soil after the 9/11 attacks—a quip that seemed to quiet Donald Trump for the rest of the debate.

The losers? Trump, who still insisted airily that he will be able to learn more about foreign policy before he’s elected president. Ohio Gov. John Kasich’s emphasis on multilateral solutions to worsening international conflicts is unlikely to resonate with an increasingly hawkish party. Wisconsin Gov. Scott Walker still needs to demonstrate he’d be ready for that 3-in-the-morning phone call. Ben Carson even suggested that Osama bin Laden could have been captured under George W. Bush had the country become “petroleum independent.”

For all the talk of the Republican Party looking past Bush’s presidency, the reality is that his foreign policy legacy is still defining today’s GOP. Republicans see terrorism and national security as being equally important as the economy, according to polling, even as it’s a secondary concern for Democrats. The rise of ISIS during Barack Obama’s presidency is only intensifying concerns that the country is at risk of another terrorist attack. The loud applause Jeb Bush received after invoking his brother’s security record was the most telling moment of the debate.

The candidates who ignore this fundamental dynamic will find themselves losing ground as voters start paying closer attention. Kasich doesn’t have to be the most hawkish candidate in the field, but failing to outline the serious concerns Republicans—and a majority of voters—have with President Obama’s Iran deal was a political blunder. Donald Trump responded to a question of whether voters would trust him with nuclear codes with a bombastic attack against Rand Paul. Carson, the other front-running outsider, looked out of his element when asked about his approach to national security. Meanwhile, Paul forcefully explained his noninterventionist posture, but it remains out of step with a majority of Republican voters.

Rubio was the clear winner on the foreign policy front. Given his youth and relative inexperience, his biggest campaign challenge has been to convince potential supporters that he’s prepared to be president. His specificity on foreign affairs questions should go a long way in making the case to skeptics. Indeed, he argued that preparation on foreign policy should be a litmus test, making that case directly to Donald Trump. “These are extraordinarily dangerous times that we live in. And the next president of the United States better be someone that understands these issues and has good judgment about them,” Rubio declared.

Fiorina was the only one of the three political outsiders running who looked steady talking about foreign affairs. Asked about how she would deal with Russian aggressiveness, she eagerly showcased her expertise (and implicitly criticized Trump’s lack of knowledge about foreign figures laid bare in a recent radio interview with moderator Hugh Hewitt). “The reason it is so critically important that every one of us know [Iranian] General [Qassem] Suleimani's name is because Russia is in Syria right now,” Fiorina said, “because the head of the Quds force traveled to Russia and talked Vladimir Putin into aligning themselves with Iran and Syria to prop up Bashar al-Assad.”

It’s no coincidence that Rubio and Fiorina received among the strongest early reviews of all the candidates—and that Bush turned his debate performance around with a resonant response on national security. The candidates weren’t quizzed on esoteric foreign policy trivia, but they were asked probing questions testing their readiness to be president. Those who didn’t pass the test, no matter their current standing in polls, will ultimately have a tough time winning their party’s nomination.

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