Libertarians and Democrats could team up to completely destroy the Republican party. Here's how:
In every Congressional race where Democrats don't have a shot at beating the Republican, they should refrain from running a candidate and, instead, back a Libertarian for the same position.
The one consistent excuse I hear from Republicans for why they voted for Trump was: Hillary. In general, it's lesser-of-two-evils rearing its ugly head. If you take away that component - if the alternative to a nationalist Trump-Republican candidate is a Libertarian - lots of Republicans will jump ship. ie If there was no danger that voting against the Trumpster candidate would elect a Democrat, lots of Republicans would happily vote Libertarian. And if there was no Democrat running, most Democrats would vote Libertarian over a Trumpster. That would likely be enough for the Libertarian to win.
Ultimately, this strategy would drive a wedge into the Republican party and offer a real choice. Even if no races were actually won, it would get Republicans thinking - do we really want to support such a despicable person?