Better question:
How many House seats (and Senate) will Dem-Financed “Libertarians” cost us?
In 2012, I stopped counting at 12 House seats we lost to Dems by less than the margin of the “libertarian” vote.
You are making the unjustified assumption that 100% of Libertarians would otherwise have supported the GOP.
In my experience, Libertarians come in two flavors. One group became Libertarians they want the government to keep their hands off their guns. The other because they dislike the government telling them who they can sleep with or what they can smoke.
Group A would probably vote GOP if they had no other choice. Group B would vote Democratic.
And of course if there were no Libertarian candidate some percentage of the Libertarian voters would just stay home.
Well, in Virginia, the “Libertarian” candidate (funded by an Obama bundler) crashed and burned BAD on morning talk radio here in DC. . .