It's ironic that you're using the term "witch hunt" here, given that term is usually used(justly)for center, center-right, and right-wing persecution of people on the left(or simply suspected of being TOO far left), rather than the expression of suspicions about people in the center by people on the left.
I oppose Mulcair for the leadership...I don't want the guy burned at the stake, let alone stripped of his passport(as Paul Robeson was)or blacklisted from all but menial employment(as dissidents in the late 1940's U.S. AND the Soviet Union were) . He'd be a great Cabinet minister(so long as he wasn't at External Affairs-he's always been too Likudnik for that position), but the leader shouldn't be a person who's reflexively hostile to the social movements, as Mulcair can be assumed to be. OK?
Besides, it's not as if he's possessed of any personal electoral magic beyond all other mere mortals...if he was, he wouldn't have come close to LOSING Outremont in 2008.