The most important element is that all of the whipping stories were based on the same videotape; there were no added sources for most of these accounts. Even if these officers were treated as "public officials" under the more difficult standard of New York Times
...which still proudly displays Walter Duranty's Pulitzer prize...
v. Sullivan, they could still make a compelling argument that the comments were made with the "actual knowledge" of the falsity or "reckless disregard of the truth." Moreover, these claims would be recognized in many states as per se defamation. While some can legitimately argue that the use of the horses was still abusive or dangerous, horses are routinely used for crowd control and these border agents were ordered to the river for that purpose.
Congressional
a poor excuse is better than no excuse at all...
their remarks in this case were made outside of protected congressional areas.
"That man is a liar, a thief, a child molester, and he pooped in my hat!... Can't touch me. I'm a congresscritter!"
Those in the media might limit their legal liability with corrections posted or published within a few days of the initial reports — but they can still be sued. It could be argued that some apparently did not care if the border agents did or did not whip