Masahiro Mori coined the term "uncanny valley" to describe that sick-to-your-stomach feeling you get when you encounter something that appears to be almost, but not quite, human. It's usually associated with robots, CGI in computer games, or Tom Hanks' creepy-looking character in The Polar Express.

In the 2016 election, there is a candidate who falls into the uncanny valley of GOP politics: Rand Paul. He is almost, but not quite, a libertarian — thus repulsing libertarians. He is almost, but not quite, a conventional Republican — thus repulsing conventional Republicans.

Is it any wonder Paul barely qualified for the prime-time GOP debate on Tuesday night?

Paul used to be the most interesting man in Republican politics. He seemed to be the next logical step for right-leaning libertarianism. He refined portions of his father's philosophy. Whereas Ron Paul's anti-war views grew out of his more general protest of the federal government, Rand Paul articulated a foreign policy that could unite non-interventionists and foreign policy realists against the party's hawks. Ron Paul had the demeanor of a professor, gripped by the beauty and purity of an ideal. Rand Paul had a mind for politics. He could turn a filibuster against America's drone policy or domestic spying into a social-media event. Expectations for his career were naturally high.

The Kentucky senator was supposed to do a lot of things in the 2016 election. He was supposed to combine heterodox thinking with a savvy media presence. He was supposed to make formerly out-there ideas acceptable to the mainstream, while loosening the grip of conservative ideology over the GOP. He was supposed to be the leading critic of George W. Bush's foreign policy. His rise was supposed to put fear into the old guard of the party. Instead, Donald Trump is doing all those things, and Rand Paul is a rounding error in the polls.

Paul could rebound. Or in some future cycle, he may find a moment that better matches his views. But right now, it very much looks like Paul will finish well behind his father's showing in New Hampshire in 2012.

Back in March, non-interventionist writer Daniel Larison explained the lack of enthusiasm for Paul by pointing to his constant compromises on the principle of non-interventionism:

It is becoming increasingly difficult to distinguish him from the rest of his party on the issues that were supposed to set him apart, and so he is bound to receive less support as long as that is the case. Paul could try to fix this, but it may be too late to undo the damage. For the sake of trying to find common ground with people in the GOP that loathe him, he has burned bridges with many of the people that were once most likely to be on his side. [The American Conservative]

Paul's father, for all his shortcomings as a campaigner, was at least willing to be hated by his enemies. When the senior Paul drew a withering and nasty attack from Rudy Guliani in a 2007 debate, many people thought the Ron Paul campaign would end. Instead, the Paul campaign began building a real following that very night.

Rand Paul has lately started beating the anti-war drums. In front of friendly reporters, Paul has assailed Marco Rubio's foreign policy as too similar to Hillary Clinton's, and dead wrong besides. He's pointed out that unlimited military spending can't be a conservative value. That's a welcome return to the Paulista spirit. But he's also probably just alienated more of his libertarian-inclined voters with a very provocative ad attacking Rubio and Ted Cruz for being too welcoming to refugees from Syria's civil war. That's exactly the sort of weaponized fear that so many libertarians loathe to see in politics. And so Paul's candidacy continues offering half a loaf to the bakery, and half a loaf to the gluten intolerant.

It's not just policy either. Paul is some sort of "halfsie" on persona as well. Political malcontents have other candidates. They don't need Paul. Even when he is not as affiliated with the liberty Republicans, Cruz is a more dramatically anti-establishment candidate than Paul seems. Donald Trump is running the larger "rebellion" from the conservative catechism and the party. What is left for a tepid candidate like Rand Paul?

By trying to be a more sensible, libertarian-ish candidate, Rand Paul has sucked the drama from his campaign. In the very long run, that may make him a more viable legislator, and in a future campaign it may make him a more viable candidate. But in this cycle, it has made him marginal.