I don't know about vulnerable/easily beaten, but it sure would be amusing.
At least he would contribute to the entertainment factor.
But there's more than just easily defeated to consider. I'd rather it were a clear choice - making it clear what Republicans stand for.
Rand Paul is similarly nutty, but his libertarian gloss makes him a better opponent to highlight the differences, I think.
They can say, oh no, as a party we don't believe those things. For instance, Paul is more isolationist than the vast majority of the republican base.
Cruz is an extremist and fanatic, but his positions are the republican positions--or what the republican base really wants the positions to be. They just differ on tactics.
They would lose. Too many racists in the party wouldn't vote for him. The Independents don't respect her.
It would be a slam dunk.
The only way it would backfire would be if all of the racists held their collective noses and voted for him to prove that they weren't racist. I think that's how Tim Scott won. Nothing else makes sense.