Ask him to explain pretty much anything.

The large Republican primary field didn’t just help Trump by allowing him to cruise to early victories with relatively modest pluralities. It also helped him in the minute-to-minute unfolding of the early debates. He could get in his insults against Jeb Bush or Rand Paul or some other foil, and then, as the conversation—as it occasionally did—ventured into more substantive policy grounds, he could go into hiding for tens of minutes at a time as, say, Paul and Chris Christie argued about surveillance programs or medical marijuana. The stage will be smaller Monday night, as Trump competes in the first one-on-one presidential debate of his life. There will be no hiding.

It’s not necessarily in Clinton’s interest to turn this into a patronizing quiz show. Voters don’t cast their ballots based on which candidates best trill the rhotic consonants in foreign leaders’ names. But there are things that people expect their presidents to know, and on this count Trump tripped up a few times during the primary debates.

In the Dec. 15 debate held in Las Vegas, CNN guest questioner Hugh Hewitt asked Trump which element of the aging nuclear triad he felt was most urgently in need of an upgrade. Trump’s response was a jumble of nonsense about Iraq and Syria that made clear he had never heard the term, which refers to land-, air-, or sea-based systems for delivering nuclear weapons. That’s not great. But it’s deeper than terminology: It was clear that he had never considered the question of nuclear arsenal maintenance. He did, however, say that, “I think, for me, nuclear is just the power, the devastation, is very important to me.” Indeed, big bomb go boom.