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

The fifth — and final Republican debate of 2015 is over.

Tuesday's Las Vegas debate featured a series of high-profile skirmishes. Ted Cruz and Marco Rubio battled over the National Security Agency and its metadata program as well as their stances on immigration. Jeb Bush went after Donald Trump hard, casting him as an unserious person; The Donald dismissed Bush as irrelevant because of his low poll numbers.

Below is my take on the best and the worst from the night that was.

Winners

* Jeb Bush: Finally, John Ellis Bush showed some spirit and fight. Jeb repeatedly took it to Trump and refused to back down amid a cascade of insults the real estate magnate launched at him. It's somewhat remarkable given Trump's clear status as the Republican front-runner — and, make no mistake, he is — that Jeb was the only candidate willing to go at the billionaire. Jeb deserves significant credit for, largely, fighting that fight alone.

The issue for Jeb is that his performance may be (and probably is) too little, too late. He has dipped so far down in national — and most state — polls that it's not immediately clear that a single strong debate performance can revivify his candidacy.

But I've criticized Bush for months for not stepping up in big moments. He did it tonight.

* Marco Rubio: The Florida senator proved (again) that he is the best natural debater in the field. Totally in control. Relaxed. Extremely knowledgeable. He won, rhetorically speaking, a face-off with Cruz over metadata and held his own when Cruz attacked him on his participation in the Senate push for comprehensive immigration reform. When Trump — more on this later — had no clue what the nuclear triad was, Rubio stepped in to flex his policy chops.

The debate focused a bit too much on his Senate record on immigration for Rubio to be a slam-dunk winner. But he reaffirmed that he is a top-tier candidate — and deserves to be.

* Chris Christie: The New Jersey governor had one goal in this debate: distinguish himself from the likes of Cruz and Rubio as someone who has never spent any time in Washington. He did so — repeatedly and successfully. He effectively injected himself into an extended back and forth between Cruz and Rubio on the NSA to say, essentially, regular people don't have any idea what the hell you guys are talking about and they don't care.  Christie went into this debate with momentum in New Hampshire; nothing he said or did Tuesday night will hurt that roll.

* 1st hour Donald Trump: Halfway-ish through the debate, I thought Trump was clearly in the winner's circle. He was measured in his responses, unruffled under attack and avoided the epic cliches — we don't win anymore, you will be so happy, etc. — that he typically falls back on.  That hour was the best hour of any debate thus far for Trump. Unfortunately for him, it wasn't a one-hour debate.

Presidential candidate Donald Trump reiterated his controversial stance on immigration and internet security during the fifth Republican debate held Dec. 15. Trump also had some heated exchanges with rival Jeb Bush, but expressed approval for Ted Cruz. (Deirdra O'Reagan/The Washington Post)

* The mystery of the coughing candidate: Okay, I probably spent too much time trying to figure out who kept coughing. But I loved "Encyclopedia Brown" as a kid — so sue me. And, yes, it was Ben Carson. (And, double yes, Philip Bump figured it out before me.)

* Ayla Brown: The former "American Idol" contestant and daughter of former Massachusetts senator Scott Brown (R) sang the national anthem before Tuesday's debate. And she was damn good.

Losers

* Ben Carson: There's no debate that Carson is a brilliant doctor. There should also be no debate that he is just not a very good political candidate.  Carson's refusal to offer an opinion on where he came down on the debate over security versus freedom — as articulated by Cruz and Rubio — was a giant head-scratcher. Time and again when asked about foreign policy and national security, Carson would say lots of words but very few of them made sense together. Aside from his opening statement, which I thought was quite good, he looked entirely out of his depth.

* John Kasich: The Ohio governor needed a moment and just couldn't find one. Thankfully he abandoned the "mad as hell and not going to take it anymore" persona he had adopted for the last debate and got back to who he really is: a committed pragmatist with an impressive record of results in Ohio. But, Kasich's ear for what this electorate wants is way off; at one point, he used his 18 years of service on the House Armed Services Committee as a proof point that he knew what he was talking about regarding national security matters. No Republican voter wants to back someone who touts his two decades spent inside the Washington machine.

* Ted Cruz: Cruz wasn't actively bad in this debate. His skills as a presenter and performer ensure he will never be genuinely bad. But he seemed to bite off more than he could chew on several occasions. His face-off with Rubio early in the debate over the NSA didn't end well for him, and his extended attempt to interrupt moderator Wolf Blitzer didn't either. Cruz got almost 16 minutes of speaking time — the most of any of the nine candidates — but didn't do as much as I expected he would with it. Not a terrible performance by any means. But short of expectations.

* 2nd hour Donald Trump: He just couldn't keep it up for the whole debate. Trump showed his thin skin when, under attack from Jeb, he dismissed the Florida governor with this polling slam: "I'm at 42 and you're at 3." Later in the debate, Trump clearly had no idea what the nuclear triad was and, in a transparent attempt to cover his tracks, resorted to his "we need to be so strong" crutch.

* Lindsey Graham: The South Carolina senator continues to dominate the undercard debates — and, as our Philip Bump argued, clearly deserves a spot on the main stage. Why is he a loser then? Because it's almost impossible to imagine him gaining enough in the polls to make the big stage before the next debate.

* Men's fashion: Eight dudes on the stage. All dressed almost exactly the same. Can someone try something other than a blue suit, white shirt and red tie? Come on man!