Read the title, don't say it, because he emphatically is not. He is one of the intellectual titans of the HBD movement. But his apparent visceral disdain for Trump renders him unable to maintain his composure when the subject in question is perceived to be anywhere near the GOP front runner's orbit. Murray earlier today (issue here):
Fully fleshing out someone's position when it is presented in fewer than 140 characters is rarely a sure thing, but I read this as insinuating that Trump supporters posture about human migration and that amnesty supporters (of which Murray self-describes himself as) need to make sure they are thinking about and analyzing it to counter that posturing.
It's unclear that Murray is even aware that John Derbyshire is an unapologetic Trump supporter. By linking to his article in this context, Murray is obviously admitting that Derb is among those who are "thinking, analyzing, not posturing". Oops.
Trump supporters are the only ones who have been doing that. Serious thinking about the National Question has been and continues to be done by people who tend to view the Trump phenomenon is a positive rather than a negative development (to put it mildly).
On the other hand, maybe I'm misreading what is intended by Murray to be humble admonishment of those of a like mind, as in "Trump sucks but he and his supporters are substantively dealing with this while we're ignoring it or serving up embarrassing boilerplate about it in the WSJ and NYT".