AT A White House meeting on Nov. 22, President Trump sent more alarming signals that he will water down his planned restrictions on flavored vaping products. After promising in September to ban flavored vaping liquids that appeal to teenagers, the president fretted that “if you don’t give it to them, it’s going to come here illegally.” He previously raised concerns about protecting “jobs” in the vaping industry.

The policy debate should focus on preventing a generation of teenagers from getting hooked on nicotine, not on the fear that efforts to protect public health will upset vapers and vape shop owners.

Vaping presents two public-health concerns. The first is what the inhalation of superheated vaping liquids does to vapers’ bodies. It was widely accepted that vaping’s long-term toll was far less toxic than that of smoking conventional cigarettes — until a spate of cases of severe lung injury. It now appears that most of the lung injuries resulted from the use of sketchy vaping liquids that contain THC — marijuana’s active ingredient — and a thickening agent known as vitamin E acetate. It is still a good bet that mainstream vaping products are less unhealthy than conventional cigarettes. But the episode underlined how the vaping industry’s relatively unregulated, Wild West beginnings might mean that not all its dangers are understood.

What we do know is that e-cigarettes contain substantial amounts of nicotine, a highly addictive substance. Yet the perception that they are low-risk products, along with the widespread availability of flavored e-liquids, has led to a surge in youth vaping — and, public-health advocates warn, a new generation of nicotine addicts. Delivered without the toxic substances found in tobacco smoke, nicotine on its own is not nearly as dangerous. Yet it still harms adolescent brains. Another worry is that, once introduced to nicotine consumption, today’s teenagers will get their fix by smoking or chewing tobacco — particularly if vaping is found to be, or becomes perceived to be, somewhat riskier than once thought.

The president announced in September that the FDA would ban all flavored vaping products — except those flavored to mimic the taste of tobacco, to which nonsmoking teenagers are not accustomed. Vaping giant Juul announced it would stop selling mint-flavored pods for its devices, which accounted for some 70 percent of the vaping pods it sold. Mr. Trump’s move would have ensured that smaller actors in the vaping industry could not fill the gap with products that appeal to children.

But Mr. Trump has apparently begun to worry about alienating vapers and their ideological allies, including a motley assortment of conservative anti-regulation zealots.

The priority should be, first, the health of today’s teenagers and, second, the health of current smokers seeking alternatives. The FDA will soon insist that vaping products undergo stronger regulatory review before they come to market, which should result in stiff restrictions on their marketing and sale designed to eliminate teenagers’ access. This is supposed to dovetail with an FDA move to cut the amount of nicotine in cigarettes, encouraging smokers, if not to quit, at least to seek alternative nicotine vehicles. The Trump administration must aim to make e-cigarettes minimally attractive to teens in the meantime. Even if a flavor ban results in a black market, it would at least diminish youth access.

The president must stick to his original promise to govern on behalf of children, not the vaping lobby.

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