But in doing so, Trump makes the same mistakes he made in the initial tweet. And in the end, it still doesn't make sense.

First, the comments, via the Deseret News (emphasis added):

Trump Jr. said the picture he tweeted earlier this week was about his concern as a father of five about what could happen "if we're not vetting people and we're arbitrarily letting them into a country."
"We've seen what's going on in Europe. We can't be naive to that and pretend that's not happening there," Trump Jr. said. "If there's one death associated with it because we messed up and we didn't do it right, that's a problem for me."
He said the tweeted picture did not represent a ratio of terrorists to refugees because he "didn't say numbers of Skittles," even though the accompanying test asks if someone would take a handful of the candies knowing "just three would kill you."

Now, to the three problems:

1) Trump says refugees are "arbitrarily" being let into the United States

While this was suggested by his tweet, Trump is now flat-out saying it. But it's just not true. The refugee vetting process is a lengthy one that can take one to two years. And people who can't be adequately vetted are turned away.

You can argue that the current refugee screening process isn't sufficient. You can argue that refugees from Syria can't be adequately vetted even with the most stringent form of "extreme vetting" possible. But Trump is basically pretending that this process doesn't exist. He's saying the Skittles are being indiscriminately grabbed from the bowl by the handful and that refugees are "arbitrarily" let in, as if the refugee process is a willy-nilly handing out of a plane ticket to Nebraska.

It's not.

2) He says he wasn't referring to a specific ratio

Since Trump tweeted this, our own Philip Bump and others have pointed to data suggesting the odds of a specific American being killed by a refugee in a terrorist attack is roughly 1 in 3.64 billion.

In other words, for every 10.92 billion years that Americans live — one Skittle, if you will — refugees will kill an American in a terror attack in three.

Trump insists he wasn't being specific about his ratio, but the small bowl pictured and the fact that he specifically said three of them were poisoned suggest he was certainly inflating the risk, whether intentionally or not. If the bowl included, in Trump's metaphor, 10 billion Skittles, after all, you can bet most anyone would gladly grab a handful or two without giving it a second thought. (I sure would. Skittles are delicious.)

3) He says he wants the risk to be zero

Of course, in the interview, Trump also suggests even one poisoned Skittle in a vat of 10 billion wouldn't be acceptable to him, because of the risk it would pose to one American life. That's also a problematic position, though, given that calculated risks are inherent in every decision made by the American immigration system.

His father, for instance, says he could be okay with admitting a Muslim immigrant from Scotland. But what if, in Trump's metaphor, the risk there is one poisoned Skittle out of 1 million? Is that still a risk worth taking? Trump seems to say no.

By that logic, the only solution is a large-scale walling off the entire United States and all of its ports, because every person coming in represents some kind of risk and could wind up killing one person.

It's a very difficult proposition to try to decide how much risk is warranted through the refugee and immigration process, but it's a calculation that is part of the process and must be balanced against the humanitarian benefit in the case of refugees and the economic benefit in the case of immigrants. No level of screening is going to be completely foolproof. And there is always a risk, in Trump's metaphor, of a poisoned Skittle no matter which bowl you grab them from — whether Syrian refugees, Scottish Muslim immigrants or American-born extremists driven by racism.

Which makes the Skittles metaphor entirely too simple for such a complex humanitarian issue, even as revised.