ObamaCare is collapsing. An entitlement crisis is looming. The national debt is exploding. And the Middle East is imploding. But somehow, the central issue driving the 2016 presidential election is what to do with about 3.5 percent of the American population that works hard, pays taxes, and delivers untold consumer benefits: undocumented immigrants.

Despite the relentless focus on immigration, the debate surrounding this issue has been awful. If Donald Trump is cruel on immigration, Hillary Clinton is cynical. In fact, the only candidate who is humane and sensible is Gary Johnson, the Libertarian Party nominee.

There's no doubt that Trump has pulled his party to a very dark place, where none of the GOP's usual qualms about the perils of Big Government apply anymore. After a brief flirtation with a softer stance, he returned to form last week, doubling down on his harsh rhetoric. He reiterated his pledge to build a big, beautiful, and "impenetrable" wall on the southern border and get Mexico to pay for it — never mind that the Mexican president told him only hours before that Mexico would never foot the bill.

Trump promised to create a federal deportation force within the first hour of assuming office to ferret out two million undocumented criminals — never mind that the Department of Homeland Security says that there are only 820,000 such immigrants. He amped up his "no amnesty" rhetoric, declaring that not only would he rescind President Obama's executive order giving some undocumented immigrants a temporary deportation reprieve, but also issue detainers to any undocumented immigrant arrested for any crime, presumably even something as minor as loitering or possession of small amounts of marijuana — never mind the terror this would inject into Latino communities. Perhaps worst of all, he's hinting at curbing legal immigration even further to protect American jobs and wages — never mind that such restrictionism is precisely the cause of the undocumented population in the first place.

But if Trump has been hysterical on this issue, Clinton has been AWOL. She barely said a peep about Trump's 10-point immigration plan. And in the past she has backed proposals that can be fairly described as Trump-lite.

Clinton has often emphasized the need to "control" borders, and boasted about how as a senator she voted "numerous times" to spend more to "build a barrier to try to prevent illegal immigrants from coming in." What's more, she's had a few of her own flip-flops over the years. During her previous presidential run, she had strongly (and rightly) condemned a federal crackdown on sanctuary cities such as San Francisco. But in the wake of the freakish killing of a 31-year-old California woman by a clearly deranged undocumented Mexican worker in San Francisco she declared that she has "absolutely no support" for a city that defies federal deportation rules — a Trump-worthy distortion of what sanctuary cities are all about. And just like Trump, she wants a biometric entry-exit system to track every border crossing of everyone — Americans and foreigners alike.

Clinton is now vaguely promising to go beyond President Obama's executive amnesty and use her presidential powers to offer deportation relief and work permits to more undocumented immigrants while pushing full-blown amnesty in Congress. But as a senator, she derailed then-New York Gov. Eliot Spitzer's efforts to issue driver's licenses to them.

Meanwhile, neither Clinton nor Trump has proposed a guest worker program, the best antidote for the labor prohibitionism that drives illegal crossings.

And that brings us to Gary Johnson.

The Libertarian nominee is the only candidate who wants the market — rather than bureaucratic "quotas" and "caps" — to regulate immigration flows, confining the government's role to conducting background checks and issuing Social Security numbers. He objects to the very term "illegal immigrant," because it implies that legality depends on papers issued by the government — an utterly offensive notion in a free society. (Come to think about it, how about calling these people "paperless workers?")

Furthermore, in a recent op-ed, Johnson, a two-term governor of New Mexico, a border state, pointed out that the ridiculous premise behind Trump's plans to militarize the southern border is that people prefer to cross the border illegally because they have nefarious motives. That's not true. The vast majority cross because they have jobs and family members waiting for them in America, but no legal options for joining them, or none that'll allow them to come here in this lifetime. "If it took months or years to get a driver's license, how many of us would throw up our hands, get behind the wheel, and take our chances driving without one?" he asks.

That's precisely why creating a fast lane in the form of a guest worker program for law-abiding, low-skill foreigners who simply wish to work and live in America is the only good solution.

This is not mere theory. Indeed, Cato Institute's David Bier has found that apprehensions of illegal border crossers between 1949 and 2014 map almost perfectly with the availability of guest worker visas — falling when these visas are more plentiful and increasing when they are not. Indeed, even a tanking economy doesn't affect illegal cross-border traffic as much as visa availability.

The big upside of a generous guest worker program is that those who don't use it can be considered by default to be criminals and cartels because who else would want to enter illegally? In other words, a guest worker program won't just be good for the economy, but also national security, something that Trumpkins claim is their primary concern.

Johnson is fighting for a spot in the presidential debates. For the sake of a rational discussion, let's hope he succeeds. If we are going to spend a ridiculous amount of attention on a non-problem like what to do with America's 11 million undocumented immigrants, at least there ought to be a sensible voice at the table — rather than letting a nasty authoritarian and an opportunistic politico dominate the discussion.