Will Libertarian presidential candidate Gary Johnson's bid for the White House go up in smoke?

Conditions are ripe for the rise of a candidate like the former New Mexico governor, who is attempting to appeal to disaffected voters by highlighting his record as a socially liberal yet fiscally conservative two-term Republican in a reliably blue state.

Both major party candidates have historically high negative ratings, and the Libertarian ticket might make the ballot in all 50 states. As Republican nominee Donald Trump sinks in the polls, dozens of prominent GOPers have indicated they'll direct their vote elsewhere.

Why, then, has Johnson struggled to attract more high-profile Republican support?

In part, Johnson's positions on marijuana use and legalization seem to be playing a role. Not only is Johnson the only viable remaining candidate in favor of legalizing the drug, but he has admitted to using it in the recent past.

Although polls show that a significant portion of the public has also indulged in marijuana (not to mention our current and two previous presidents), this appears to be a bridge too far for some prominent Republicans who might otherwise have been open to him. Just one Republican official, Rep. Scott Rigell, has announced he'll vote for Johnson.

Maine Sen. Susan Collins, one of the most prominent anti-Donald Trump Republicans, has said she wished Johnson was not at the top of the Libertarian ticket because she is "concerned" about his position on marijuana.

Former GOP presidential nominee Mitt Romney, another vehement opponent to Trump, has offered the same sentiment. Marijuana “makes people stupid,” Romney told CNN in June. He said he could have easily supported the Libertarian ticket if Johnson's vice presidential pick, moderate former Massachusetts governor William Weld, had been chosen as the standard-bearer.

Rep. Charlie Dent (R-PA), who opposes Trump and says he will not support Democratic nominee Hillary Clinton "under any circumstances," has also drawn the line on Johnson over the drug issue.

"I think Gary Johnson's made some statements ... something like he's not going to smoke dope between now and the election. That's not particularly encouraging or inspiring," said Dent during an appearance earlier this month on MSNBC's "Andrea Mitchell Reports."

Although Dent admitted to not knowing Johnson, he, too, said he'd feel more comfortable if the ticket were "reversed," with Weld as the presidential nominee.

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For the record, Johnson has vowed not to use marijuana or drink alcohol while he is campaigning (although there has been some dispute over when he has stopped) or if he becomes president. NBC News has reached out to Johnson's campaign for comment, but has not heard back at this time.

According to Ethan Nadelmann, the executive director of Drug Policy Action, a non-partisan political advocacy group, Johnson's critics often fail to see how serious he is on the issue of reform.

As a Republican governor, Johnson earned a reputation for being swift with his veto pen, especially when it came to spending bills, but he broke ranks with his party on marijuana legalization and worked with Democrats in the state legislature to increase funding for drug treatment.

"I felt that Gary Johnson was courageous and bold," Nadelmann told NBC News. "He was a real role model for responsible leadership on drug policy reform."

Nadelmann believes that Johnson deserves credit for being ahead of the curve on drug policy at a time when members of both parties were skittish about the issue. Now, as a national candidate, Johnson is also breaking ground by admitting recent recreational drug use, instead of passing it off as a purely youthful indiscretion.

"It's the evolution from a president who said I smoked but I didn't inhale ... to people beginning to say 'Well, yeah I use it, what's the big deal?' I think we'll see more people doing that," Nadelmann said.

Certainly, it appears that the American public has become increasingly more comfortable with drug use and legalization than some of their elected officials. According to a recent Gallup poll, one in eight adult Americans (13 percent) say they use marijuana, and nearly half the country (43 percent) has at least tried it.

This number represents a dramatic and steady rise from the 4 percent that admitted using marijuana when Gallup first began polling the public back in 1969. Meanwhile, a Quinnipiac University poll in June found that a majority of Americans (54 percent) now support marijuana legalization. It's another sea change in public opinion that some attribute to the open-minded approach of President Barack Obama, but also could indicate a populace more educated about the potential health benefits of the drug.

Jeffrey M. Zucker, president and co-founder of Green Lion Partners, a business strategy firm working to the elevate the public perception of the legal marijuana industry, is on the front lines of that fight.

The Colorado-based 28-year-old believes that while stopping Trump from becoming president is probably his biggest priority, he is currently leaning toward supporting Johnson in November in part because of his position on marijuana.

"He is the most sane and logical of the three candidates and what he says for the most part resonates with me," Zucker told NBC News, with the caveat that if he feels his home state state could swing towards Trump, he's willing to back Clinton. "I respect and appreciate [Johnson's] acknowledgment of consumption and the cannabis industry. It's good to change the conversation. There are adults all over the world who use marijuana and are perfectly happy and capable people."

But that premise continues to be met with resistance from GOP officials and voters.

"It's just going to take time. It’s going to continue to be a state’s right issue for awhile, and in the next three to five years it will be a national issue," Zucker said. "I hope they will eventually come around … or this generation will be in charge by then."

Nadelmann believes that generational bias is definitely a factor in Republican recalcitrance on marijuana reform. He points that even though most Republican millennials are in favor of legalization, less that 50 percent of that party nationally backs reform.

"For many of them, as they court older voters, I think it's seen as a safe decision for them in 2016. I am sure that will evolve in the coming years," he said.

In his opinion, statements from politicos like Collins are "silly" because they fail to see they are on the wrong side of history. Nadelmann argues that while marijuana is currently viewed as a "young person's issue," the face of users and advocates is evolving as more elderly Americans see the benefit of medical marijuana. He cautions that it's not just Republicans who could pay a price for not getting on board.

"Hillary has reassured people at Democratic fundraisers that she will be at least as good as Obama was on drug policy and publicly she has followed his lead," Nadelmann said. But he also thinks she has been "fundamentally cautious," which could cost her some crucial votes come November.

"The question will be, 'Where do they live?' Voting for Johnson in New York or Mississippi is a very different thing than voting for him in a swing state," he said.

Related: Drug Enforcement Administration Will Not Call for Reclassifying Marijuana

Still, he believes Clinton, who signed a strongly-worded pro-reform statement to the United Nations in April, is widely perceived by advocates as preferable to Trump. The Democratic Party endorsed a platform plank that called for a "reasoned pathway to future legalization. Meanwhile, the Republican nominee has surrounded himself with people like Gov. Chris Christie and Gov. Mike Pence, who have both been hostile to efforts to legalize marijuana.

Drugs usually don't rank anywhere near the top of voters' concerns, and Johnson's views on marijuana may not endear him to Republicans on the fence. But receiving the endorsement of the largest national organization in favor of marijuana legalization (as Johnson has) might persuade someone like Zucker.

How could Clinton win his vote? "I think she hasn't been that outspoken on cannabis," Zucker said. "I think if she took a hard stand against the drug war and if she really stood up for the industry and the patients involved, that could make a difference."

"The bottom line is everybody is using cannabis everywhere," he added. "It might as well be safe, regulated and taxed."