There is a lot of Republican -> Libertarian and Republican -> Independent switches going on, probably more to independent then libertarian. And the Democrats are not picking up very much, in fact more are leaving then joining. Few Democrats are going Libertarian though, it is mostly Independent or Green.

At one time there was a Democratic leaning chunk in the Libertarian party, but since the Green party has begun to build up some strength in the US that has faded.

Because of that the US is moving towards a situation where the Libertarian party is the "Conservative but can't support the Republicans" party and the Green party is the "Liberal but can't support the Democrats" party.