Libertarians are rightly known as being social liberals and weak on defense, it is why they oppose conservatism.
Rand Paul sounds like a democrat because of his libertarianism.
A lot of supposed conservatives, however, have made their peace with the welfare state and strongly support programs like Social Security that were anathema to the conservatives of the FDR era, for instance.
As I pointed out on a thread last week there is a long history of the GOP being non-interventionist, including many prominent GOP politicians opposing US entry into WW1, and involvement in WW2 prior to Pearl Harbor. You might disagree with these positions, but to characterize them as "liberal" and "Democratic" is historically inaccurate.
The proclivity for starting wars when not essential as many feel Bush (the younger) did - comes from the neoconservative outlook. Although, TR was a bellicose militarist too, and a Republican.