“The downside for the Republican is that conservatives will vote for the Libertarian because they can’t stomach voting for anyone except their original choice.”
Damn, there IS a problem with liberty, We must change this - May I suggest we enforce Thought Control on these recalcitrant conservatives :)
Voting for someone who will not win is sometimes satisfying and may even serve to send a message. Good strategy when the outcome is not in doubt. When it is, you need to be mindful of unintended consequences. How many people voted twice for Ross Perot and how did that work out for them? would we be worrying about Hillary if Bill had never been elected?
The Libertarian won't win 9 percent. Voters might prefer a Libertarian candidate to a Republican, but understand that they might as well vote for the Democrat, or not at all.
In the voting booth, most people will "satisfice" their vote, rather than "optimize" it.