From a reader:

This is not a big deal, and I think conservatives will look silly if they try to make it one.
I think it is completely fair to say this guy deserves ridicule because he can’t come up with his own ideas, or even language. But this is not the same as journalistic or academic plagiarism. This guy was not (a) using it for commercial purposes (as a journalist or other published writer is), which would be theft, or (b) defrauding himself and others re: his education (remember, the victim in academic plagiarism is not the professor; it’s the student (and his peers if they are being graded on a curve)).
Should he have sourced it? Of course. But this is neither theft nor fraud; it’s just laziness and discourtesy. And the victim of the discourtesy doesn’t even seem to care.

And from another:

Jonah,
I am an academic, and so the plagiarism issue weighs heavily with me.
The issue is not whether or not Newman cares if his material was attributed. The problem is that by publishing or signing a letter, Brown is claiming that the work is his own. I care if my students cite works in the public domain because I want to know what is original thinking on their part and where they are following someone else (even if that work is in the public domain). It is a question of whether or not the ideas (and words) are the author’s own or not. I assume that when someone writes something, the ideas and words are their own if there is no attribution. In academic circles, that is the normal assumption. Why it should be otherwise for politicians (or, as you note, construction workers) is beyond me.
If you should choose to post any of this, please withhold my name and institution.