One of the great traits of many Americans is that they want to be kind and they want to be affirming. They even have a constitutional right to pursue happiness.Trueman is actually, in my opinion, a brilliantly good scholar. Not joking. I've also witnessed Andrew Sullivan, another very smart British expatriate make the same error. And in a similar context (LGBT rights; though Sullivan was discussing same sex marriage if I remember it right).
Of course the US Constitution doesn't say that men have a "right" to pursue happiness, like it says we have a right to freedom of speech or free exercise of religion. Rather the Declaration of Independence asserts it.
But I do see some truth to the assertion. It's the notion that the D.O.I. is part of the organic law of the United States and has some authority as law in constitutional interpretation.
This is a contentious assertion. And as such it requires an argument. Timothy Sandefur makes the argument. Others have made it before him. I think the fact that smart folks like Trueman and Sullivan could have something like that roll off their tongues so instinctually supports the argument. Something was in the "air" back then. I think that's what it means to be "organic."