Here are highlights from CNN's Republican presidential debate on Dec. 15 in less than two minutes. (Sarah Parnass/The Washington Post)
Columnist

The Republican presidential debate here was actually a three-part contest: pop quiz, cage match and actual policy debate.

Donald Trump and Ben Carson flubbed the quiz, although their performances won’t matter, for different reasons. Jeb Bush, punching above his weight, won the cage match against Trump; that helps Bush’s struggling campaign, although probably not enough.

Finally came the real debate, and one that is certain to continue, over how to deal with the Islamic State specifically and how aggressively to intervene in foreign disputes in general. This event featured Marco Rubio against Ted Cruz, a pairing I expect will dominate the remainder of the campaign, with a touch of Rand Paul.

Think of the rest of the field as a kind of Greek chorus. Carly Fiorina and John Kasich piped up to croon ineffective arias to civility and adulthood. Chris Christie chimed in to note that no normal person wants to hear all that eye-glazing Washington talk and to remind us, about a dozen more times than necessary, that he is a former federal prosecutor. (I thought Republicans attacked Democrats for seeing the war on terrorism with a law enforcement mentality, but never mind. You go for the presidency with the résumé you have.)

Trump actually had two shots at the pop quiz, both of which he failed — despite having been prompted with elements of the answer. Radio host Hugh Hewitt asked Trump what his priority would be among aging nuclear forces, and Hewitt named the components of the triad: B-52s, missiles and submarines.

Trump blustered about the need for a trusted leader, about his opposition to the war in Iraq, about how “nuclear changes the whole ballgame,” about the risk of “some maniac” obtaining a nuclear weapon. Hewitt tried again, asking Trump his priority.

“I think, for me, nuclear is just the power, the devastation is very important to me,” Trump offered, incoherently. As if one were needed, there could not be a clearer illustration of his unpreparedness for the presidency. As if that might make a difference to Trump supporters.

Carson’s quiz question was even gentler. After Rubio and Paul went at it over governmental surveillance powers, Wolf Blitzer asked Carson which one was right. Having just complained that he had to wait too long to be questioned, Carson then passed at answering the one posed. “I don’t want to get in between them.”

Translation: I have no idea what this metadata argument is about. Impact: minimal. Post-Paris, post-San Bernardino, Carson is already toast.

The Bush-Trump clash provided the best theater of the night. Bush started the fight, calling Trump a “chaos candidate” and telling him “you’re not going to be able to insult your way to the presidency.”

Trump responded with juvenile camera mugging and even more juvenile my-poll-numbers-are-bigger-than-yours taunting. In a rational world, this episode would help Bush and hurt Trump. But this is GOP primary politics, 2016.

Except that an actual policy divide did emerge here, between Rubio and Cruz, over government surveillance, immigration and, most interesting, the wisdom of U.S. intervention to topple dictators. The contrast was striking, with Rubio occupying the establishment conservative role and Cruz staking out a far more isolationist stance.

Rubio accurately accused Cruz of making it more difficult to detect terrorists by opposing renewal of the government’s bulk collection of telephone metadata. Cruz misleadingly claimed that intelligence agencies were better off under the new rules.

On immigration, both candidates fudged. But it is clear that Rubio supports an eventual path to legal status for those here illegally, which is the only logical position; Cruz went further than previously in renouncing any such (decent) intentions.

And on the U.S. role overseas, Rubio correctly explained that airstrikes alone cannot dislodge the Islamic State; Cruz airily called for carpet-bombing the Islamic State, as if that could be done without massive civilian casualties.

Most alarming, Cruz argued that the toppling of Libyan leader Moammar Gaddafi and Egyptian President Hosni Mubarak was bad for the United States — as would be the departure of Syrian President Bashar al-Assad. “If we topple Assad, the result will be ISIS will take over Syria, and it will worsen U.S. national security interests,” he said.

Rubio noted that Assad “is one of the main reasons why ISIS even exists to begin with,” though he added, rather mildly, that he “will not shed a tear” over Assad’s departure.

This is an important debate, worth pursuing amid the circus that is the Republican primary campaign.

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