Libertarian nominee for president Gary Johnson sits down with the Washington Post and explains why the political climate in 2016 is ripe for a third party candidate. (Adriana Usero/The Washington Post)

GARY JOHNSON and William Weld, the Libertarian Party nominees for president and vice president, respectively, brought their fiscally conservative, socially tolerant message to an interview with us Thursday morning. In some areas, their honesty and resistance to poll-tested polish have a certain bracing appeal. Mr. Johnson had no apparent qualms about calling for some politically dicey policies, such as raising the Social Security retirement age to “at least 70” and encouraging government programs that would test heroin quality in order to reduce the number of overdose deaths. He and Mr. Weld declined the opportunity to attack one of their rivals, Hillary Clinton, over her State Department emails, saying that FBI Director James B. Comey was right to recommend against any indictment.

But this refreshing honesty could not cover up the ticket’s defects and lapses. These start with a lack of general knowledge and preparation. Mr. Johnson, the genial former governor of New Mexico, could not tell us what share of the economy the federal government should spend, only that “whatever the current level is,” it should be reduced “by a few percentage points.” He did not know what the nuclear triad is, which, though admittedly alarming in a potential commander in chief, might have been at least understandable if Donald Trump had not infamously muffed the same question in December. The two former Republican governors promise to govern in partnership, but they appeared to disagree on many fundamental issues.

None of that is necessarily disqualifying in this extraordinary political year. Mr. Johnson surely could get up to speed in some areas he hasn’t thought much about. Indeed, he and his running mate mentioned that they are getting briefings from the Cato Institute, a libertarian think tank.

More disturbing for anyone inclined to take this candidacy seriously was Mr. Johnson’s habit of resorting to wishful thinking whenever reality collided with libertarian ideology. Getting the government out of the way, he claimed, would solve a range of complicated social problems. Police shootings and various racial disparities have been results of the war on drugs, he argued, as if racism and police brutality would not exist if marijuana were legal. Climate change is real but regulations to cope with it aren’t needed, because consumers will demand clean energy, as if transforming the energy system were as simple as buying fair-trade coffee.

The Islamic State is a danger, he acknowledged, but he suggested it will work its own way into oblivion; no need for U.S. troops to help in that process. And he would solve the nation’s health-care challenge by abolishing most health insurance. “We don’t have grocery insurance,” he said. “If we did, why would there be any pricing on any of the shelves? You’d just pick out filet mignon.” With people paying out of pocket at “X-Rays R Us” and “Gallbladders R Us,” he said, prices would drop dramatically. But he also made clear he would balance the budget by letting states restrict eligibility for Medicaid, the health coverage program for the poor and near-poor. In his world, it’s not clear they could afford even a cut-rate gallbladder.

In short, Mr. Johnson offers simplistic solutions to many complex problems. Voters hoping to find a serious, attractive alternative to this year’s presumptive major-party nominees are apt to be disappointed in what he is trying to sell.