Is it good campaign strategy to SAY that Clinton won’t be able to govern, because we won’t let her, so don’t waste your vote on her??

Ah, yes, the GOP "mobster" strategy of influencing voters.

"That's a nice government you've got there. It'd be a shame if something broke it. But, you know, things break don't they, guv'ner?"

We can only hope people don't fall for that BS....:-P....

Good campaign strategy for whom? The Republicans? Yes. For Democrats? No. That is called suppressing the vote. 
Besides, Democrats could take the Senate if more Democrats vote.