The parties have been able to control who got enough exposure and popular support, to prevent intramural warfare from breaking into view. Ron Paul's campaign came the closest in the past, but Paul didn't have anywhere near the level of popular support that Trump has.
I assume Manafort's appearance on Fox coincided with the time he aired on ABC. i assume his message was the same in both places, with the only difference being the questions from the interviewers. Not that the questions would be much different!
Thanks for loaning me the reporter badge, it's an honor. I'll return it in good shape.