This time a year ago, there was talk conservatives and libertarians finally might be ready to truly join forces on an agenda to win the 2016 elections and govern as principled believers in limited government. The libertarian wing of the Republican Party – which certainly doesn’t include all libertarians – had a respectable candidate for president in Rand Paul. Another candidate, Marco Rubio, seemed open to libertarian ideas on immigration, as indicated by his participation in the Gang of 8 proposal for immigration reform. But the longer this campaign has gone on, the more the strains of the relationship have...