This kind of blackmail is older than the hills, and an insult to the intelligence. Lesser-of-evils voting is how we got into this mess.
Give people something to vote FOR and blackmail becomes unnecessary.
Given our electoral system one has several options to vote strategically. If you vote in a state where the odds strongly favor one party or the other, you can register your protest by voting for a third party or write in your own choice. In states likely to be toss ups your vote truly counts and one must live with one’s self if the most evil candidate is elected,
In the 2008 general elections, if more of our side had voted for the "lesser of two evils", we might be talking about President Palin by now. Instead we've had two terms of Obama, and might get Clinton. That's where not voting for the lesser of two evils got us.