Without knowing what's in there, it's really hard to make a call on that information alone.

This could be anything from "Hey, the source for this information is notoriously unreliable and doesn't meet our standards" to "He can't publish this because then Trump might win and that's not worth the cost". One is a very valid reason to refuse to publish something, for the other, the ends don't justify the means and he's right to be upset.