It's terribly simple. Not even about R/D. Any vote that is not for someone who could actually beat Hillary is essentially a vote for her.
It's no different with those who abstain. We can either beat her or stand back and let her win, just like we did with Obama.
Then please, tell me how this is different:
Any vote that is not for someone who could actually beat Trump is essentially a vote for him.
Democrats have to see this the exact same way. If you vote third party, you're "letting Trump win."
But, no, a vote for someone other than Trump is not a vote for Hillary. It's just a vote for someone other than Trump and Hillary.
Unless you specifically concede that Trump is and always was a loser... and shouldn't have been the Republican nominee if they wanted victory. I'm just saying that because I haven't followed where your candidate allegiances have been, I honestly don't know