It is considered poor form for a journalist (even a blogger) to not identify himself and his agency, paper or channel, prior to beginning an interview. Even an ambush-interview like this one.
The proper response from the Congressman, however, is not to assault, initiate false imprisonment or false arrest (grab the arm and fail to release on demand), or batter the interviewer.
A tasteless interview, with a response that is a byproduct of tasteless interviews.
And one other thing: For all we know, the cameraman was wearing something very provocative and intended to get a rise out of the Congressman. A dead donkey getting peed on by an elephant, printed on a T-shirt, or something along those lines.
Doesn't excuse the Congressman's actions and I think criminal assault charges should be filed against him and a civil suit initiated.