Aren't politicians like Ted Cruz and Rand Paul allies in the struggle for liberty?

Although I'm an atheist and a novice Objectivist, I've always wondered why so many advocates of individual rights oppose candidates and movements that seem to agree with us on a great many issues. Despite their other warts, Rand Paul and Ted Cruz are the most likely men to promote our causes. The notion that they evangelize is dubious. And even if true, are there better alternatives today? I've also seen this attitude towards Libertarian candidates and their party. Ronald Reagan was the only President who advanced the ball towards free markets in the last fifty years, and yet people condemn him because of his position on abortion and because of his religious/political partnerships. I've never understood this. Shouldn't we embrace the advocates of free markets out there today, even if not perfect?