Would this be a witch hunt? 
I don't know for sure that he is guilty, and I'm reserving judgement. I was just pointing out that he was indicted.
To be honest, I think that a charge against him for 'being a foreign agent' may not be a clearcut as if a regular person was accused of being a spy. For a regular person accused of being a spy, they basically set out with malicious intent. But for Senator Menendez, dealing with Egypt was part of his official duties. So it's possible that he went over the line, and did criminal activity, but it may be more 'excusable' than a regular person spying.
I don't know the precise allegations. It's possible that he is a full blown traitor. But I would be able to understand if he is not a traitor, but rather someone who stepped out of line or made a poor decision.
In short, this is similar to
the argument I made for a police officer who shot someone - since it's their job to sometimes shoot someone, it should not be dealt with as severely as someone who has no business having a gun in the first place.