Tonight Hugh Hewitt stumped Donald Trump with a question about America’s nuclear “triad” and which parts of it he felt needed the most attention. After stammering through an answer about the importance of containing nuclear threats from Syria, Sen. Marco Rubio politely explained the terminology. Here’s that exchange:

HEWITT: Mr. Trump — Dr. Carson just referenced the single most important job of the president, the command and the control and the care of the military forces. The triad, the missiles and submarines are aging out. It’s an executive order. What is your priority?

TRUMP: Well first of all, I think we absolutely need someone we can trust who is total responsibility who knows what he or she is doing that is so powerful and so important. And one of the things that I’m frankly most proud of is that in 2003, 2004, I was against going into Iraq because you are going to destabilize the Middle East. I called it, I called it very strongly and it was very important. But we have to be extremely vigilant and careful when it comes to nuclear. Nuclear changes the whole ball game. I would have said get out of Syria, get out. If we didn’t have the power of weaponry today, the power is so massive that we can’t just leave areas that 50 years ago or 75 years ago we wouldn’t care, it was hand-to-hand combat. The biggest problem this world has today is not President Obama with global warming, which is inconceivable, this is what he’s saying. The biggest problem we have today is nuclear proliferation anding are some maniac, having some madman go out and get a nuclear weapon. In my opinion, that is the single biggest problem that our country faces right now.

HEWITT: Of the three legs of the triad though, do you have a priority?

TRUMP: For me, nuclear, the power, the devastation, is very important to me.

HEWITT: Senator Rubio, do you have a response?

RUBIO: I do. Well first, let’s explain to people at home what the triad is. Maybe a lot of people have not heard that terminology before. The triad is the ability of the United States to conduct nuclear attacks using airplanes, using missiles launched from silos from the ground and from our nuclear subs. And it’s important, all three are critical. It gives us the ability at deterrence. Now, some are more critical than others. For example, the submarines. And that’s the Ohio class submarine that needs to be modernized. The air component also needs to be modernized. The B-52, as someone earlier pointed out, is an outdated model that was flown by the grandparents of the people flying it now. And we need a serious modernization program of our [cyber launch?] missiles as well.