Johnson-Weld 2016? A lot of American voters will give the Libertarian Party ticket nominated this weekend a closer look than usual this year, because of dissatisfaction with the major party alternatives.

I’m one of them. To me, it’s not a big surprise that Hillary Clinton showed up at Donald Trump’s latest wedding. The two unfortunately have a lot in common. They both oppose President Obama’s Trans Pacific Partnership free trade deal. They both favor raising taxes on “carried interest” earned by managers of investment partnerships. They both engage in the politics of blame — Donald Trump targeting Mexicans and Muslims, Hillary Clinton demonizing fossil fuel and pharmaceutical companies.

Appealing, by contrast, are the two former governors — Gary Johnson of New Mexico and William Weld of Massachusetts — running with an optimistic, pro-growth, small-government message that emphasizes low taxes, free trade, and relatively unrestricted immigration.

To close the deal with me, though — and, I’d venture to say, with a lot of other political independents — Messrs. Johnson and Weld are going to have to provide some reassurances when it comes to national defense and foreign policy. So far, what they’ve provided has been disappointingly vague or misguided, a kind of sloganeering.

In an interview over the weekend with Reason magazine’s Matt Welch, Governor Weld complained of “intervention creep” and vowed, “no more boots on the ground. No more blood on the soil.”

Mr. Weld might be asked if he regrets the Allied invasion of Normandy, and if he would have approved it if he were president. What about the American Special Forces mission that killed Osama Bin Laden? Would he bring home all the American troops currently stationed in Germany or in South Korea?

Is he satisfied with the outcome of America’s non-intervention in Syria — where 400,000 individuals have been killed, 3 million or 4 million refugees have fled the country and another 6 million or 7 million are internally displaced? How would Mr. Weld respond to a repeat of the terrorist attacks of September 11, 2001? How about to ISIS videos featuring Americans being beheaded? What level would he propose for the American military budget?

In the past, Mr. Weld has sounded different on these matters. On October 29, 1996, debating Senator Kerry, Governor Weld said, “Most of the people I have talked to have been acknowledged experts like Henry Kissinger, George Shultz, Colin Powell, Richard Haass. … I am an internationalist by outlook. I would not be leading the charge against funding for the United Nations…

“I think we should be prepared to engage militarily where our national security interests are involved. Those may be territorial or military, they may be economic…I am not one of those that thinks that foreign aid is evil, that the Agency for International Development is evil. I would not be leading the charge to undercut those agencies. I think they do a serious good job for our country.”

In a debate in September of 1996, Mr. Weld reportedly warned against going too far in cutting defense spending. He said then, “We need to be ready to fight a two-front war anytime, any place.” Back then, he wasn’t talking about the need to avoid boots on the ground.

Nor is there much reassurance on these issues provided at the top of the Libertarian ticket. In 2012, Mr. Johnson reportedly complained about Republicans: “I cringed at a lot of what they said, whether it was abortion, the terrorist threat, the homophobia, the ‘illegal immigrant is the source of all our problems’—man, that stuff made me crazy.”

Maybe the terrorist threat appeared strictly theoretical to someone from New Mexico. But after September 11, 2001; after the Boston Marathon bombing, after San Bernardino, after the attacks at Paris and Brussels — well, after all that, a politician who wants to get elected rather than just get attention will need to do more than just cringe at talk of the Islamist terrorist threat. He or she will need an actual strategy for defeating it, defusing it, or defending against it.

To a recent question about whether, as president of the United States, he would have entered World War II, Mr. Johnson replied, “I don’t know.”

Maybe the Libertarians are aiming to lure the fascist faction away from Trump?

The Libertarians are hoping that Johnson-Weld polls high enough that the party reaches the threshold for inclusion in the prime-time, televised presidential debates. If Mr. Johnson does make it onto the stage, Hillary Clinton or Donald Trump will shred him on that World War II point. On Memorial Day, let it be said unequivocally that the correct answer is “yes.”

Mr. Stoll is editor of FutureOfCapitalism.com.