Matt Yglesias points out the obvious but important fact that Trump is entirely unqualified to do the job he’s campaigning for.

Trump, it turns out, doesn’t really understand anything about how the American government or American public policy works. That the former host of The Apprentice isn’t really up to speed when it comes to the details of managing public affairs is a bit dull and unsurprising. But it deserves to be front and center in a campaign in 2016.

Above and beyond the wilder and more outrageous sides of Donald Trump’s history and persona is the simple fact that he has no idea what he’s talking about. You wouldn’t ask Barack Obama to pilot a submarine — he has no idea how — and Donald Trump has no more business piloting the ship of state.

He doesn’t even know how to do something as basic to the job as talk coherently. He exclaims and interjects and bounces from one thought to the next within a single sentence. He talks like a toddler on a sugar high. He’s a hot mess.

Policy issues were not really central to the second debate any more than they were to the first debate or, really, the entire 2016 campaign. Once again, we sat through an entire 90-minute debate in which nobody was asked about climate change. Once again, Clinton’s main argument was about Trump’s character and temperament and Trump’s main argument was about Clinton’s honesty and insider status.

But the presidency is important largely because the president is an important policymaker. And Trump has no grasp of any policy issues — he can’t describe his own tax plan, and in an answer about judicial nominations he didn’t seem to know the names of any of the people on his own short list.

That’s what servants are for.

Nobody — even the best presidents — is conversant in every policy issue under the sun. But Trump appears not to be conversant in any of them. And he doesn’t care. When his ignorance is revealed, he doesn’t study up and do better next time. He figures it doesn’t matter and he moves on.

But try to picture a man serving as president who has no idea what he’s doing. A man who doesn’t understand why a junior senator can’t unilaterally change the tax code, or that Russia has had nuclear weapons for a long time, or who regulates health care, or what a safe zone is, or where Syrians come from. It’s alarming. And even while people strive to stay shocked by the most outlandish of Trump’s behaviors, it’s also worth stayed focused on his most banal failings — he’s a rich kid and reality television star who seems somewhat talented at bilking people out of money, who for some reason wants to be president.

Wants to be, and is not at all abashed at the fact that he knows nothing whatsoever about it.