My disdain for Cockburn goes back to 1995.  I was at the Union Industry Show in Detroit, which was put on by a department of the AFL-CIO.  Cockburn wrote a piece criticizing it on something like 6 issues.  Every single one of his assertions was false.  Honestly, I don't think he even attended the thing, I think he got his information second-hand.  With that experience in mind, I was very skeptical of most of what he wrote, and often found his sourcing deplorable.  

I think Cockburn starts with his conclusion, then tosses in details to support it.  Whether the details are accurate or even real doesn't seem to bother him.  And like Raimondo, I think he's got some issues with antisemitism.  

I also have heard from someone I completely trust that he's a cad.  Maybe that shouldn't reflect on his writing one way or another, but I think it reinforces that integrity and honor--important factors in the creation of a writer's ethos--aren't among the man's strong points.