Former President Donald J. Trump’s appearance before the Libertarian Party on Saturday was without modern precedent: the presumptive nominee of one party addressing the convention of another.
They're libertarians. They vote for Republicans because when it comes right down to it, a libertarian is just a Republican who got tired of being taken seriously.
Realistically any Libertarian dedicated enough to show up to a party conference is probably a member of the 1% of the US population that votes for them in general elections.