I'm not sure that two books constitute a trend, but I should draw your attention to Murdering Mr. Lincoln: a new Detection of the 19th Century's Most Famous Crime by Charles Higham. Higham puts McClellan at the center of the conspiracy, which is a topic we'll return to next week, perhaps. That's not the interesting part; what is significant is that, according to this review, the author has picked up on the motive developed in Dark Union: The Secret Web of Profiteers, Politicians, and Booth Conspirators That Led to Lincoln's Death.
Both books tie Lincoln's assassination to the through-the-lines cotton trade, Dark Union specifically to one massive deal gone bad. Congress called Lincoln's trading permissions "illegal" and in investigating his involvement discovered hundreds of permits signed in his hand. Quite apart from the assasination, this is a fascinating piece of Civil War history not normally encountered in the master narratives.
We find, for example, in the Library of Congress's Lincoln Papers online, a letter by General Frank Blair to his father complaining of cotton trading with the rebels being facilitated by General Irvin McDowell's brother, acting as a Treasury agent. This was at a time when Gen. McDowell was the government's high commissioner for reviewing and approving deals relating to captured cotton.
So, shine the light of pop history on this ... maybe the scholars will rally to do the study this topic deserves.
p.s. Here is another pop historian (name of McPherson) reviewing Dark Union while studiously avoiding mention of the cotton business.