In 2009, not extended right after Dr. Margaret Hamburg became commissioner of the Meals and Drug Administration, a package arrived at her residence. Inside was a clunky device referred to as an e-cigarette.

“It was my initially exposure to this emerging, new technologies,” Dr. Hamburg recalled.

The package was sent by an antismoking activist as a warning about a solution that was taking off in the United States. But more than the subsequent decade, the federal government — across the span of two presidential administrations — permitted the rise of a largely unregulated sector that may perhaps be addicting a new generation to nicotine.

E-cigarettes and vaping devices, with $7 billion in annual sales, have develop into a aspect of day-to-day life for millions of Americans. Youth use has skyrocketed with the proliferation of flavors targeting teenagers, such as Bazooka Joe Bubble Gum and Zombie Blood. And almost 1,300 persons have been sickened by mysterious vaping-connected lung injuries this year.

However the agency has not vetted the vast majority of vaping devices or flavored liquids for security.

In dozens of interviews, federal officials and public well being professionals described a lost decade of inaction, blaming an intense lobbying work by the e-cigarette and tobacco industries, fears of a political backlash in tobacco-friendly states, bureaucratic delays, and a late reprieve by an F.D.A. commissioner who had previously served on the board of a chain of vaping lounges.

The agency then spent five years trying to issue regulations that would survive further legal as well as political scrutiny by a White House that had other priorities, including rolling out the Affordable Care Act.

Then, in President Obama’s last year, the administration rejected a proposal to ban flavored e-cigarettes. It came in the face of fierce lobbying over the tobacco regulations, including by a former senator and by a onetime White House analyst who had represented the Obama administration in the same discussions a year earlier.

Even bigger changes to the e-cigarette industry might be on the way. That deadline Dr. Gottlieb extended has been overturned by a judge, who ordered the F.D.A. to require e-cigarette companies to apply for approval by May, and to submit evidence their products do more good than harm. Last week, Reynolds American began the process, filing its application with the F.D.A. for VUSE, the company’s cartridge-based vaping system that features flavors such as mixed berry, tropical, menthol and others.

One of the tobacco industry’s fiercest critics, Senator Jeff Merkley, Democrat of Oregon, had urged the agency beginning in 2009 to rein in nicotine vaping products, and mentioned allies like Mitchell Zeller, who oversees tobacco at the F.D.A., and who was among the early advocates for a ban on flavors.

Dr. Hamburg, who left the F.D.A. in 2015, said the agency struggled to move quickly to issue the broad regulation for e-cigarettes as well as other tobacco products, including cigars. It was a complex process, she said, given previous court challenges.

“For something so important for health, the delays at H.H.S. and the White House were distressing and confusing — people were getting very frustrated,” she said, and given the expanding industry, “I wanted to get it out, from a reputational point of view and from a morale point of view for F.D.A.”

At the time, the Obama White House and the Department of Health and Human Services were also dealing with mounting Republican opposition to the administration’s signature health care law, the Affordable Care Act, which was passed in 2010 and went into effect in 2014 with an exceptionally bumpy rollout.

In Congress, the tobacco industry lobbied hard against the proposals, using its pull as a major donor to get Republicans and some Democrats to sign on to industry-friendly bills.

Shaun Donovan, the director of the budget agency, and other Obama administration officials, including Kathleen Sebelius and Sylvia Mathews Burwell, both of whom served as secretary of the Department of Health and Human Services during that period, declined to comment. Dr. Robert M. Califf, who had supervised policy on tobacco products at the F.D.A. before becoming commissioner in 2016, said he did not know why the flavor ban had been deleted. However, “I’m sure the small business impact had something to do with it,” he said.

Dr. Hamburg, who had left by then, also said she did not know why it had been deleted.

Some former Obama administration officials said the White House considered the flavor ban too restrictive and that there was no solid evidence that flavored e-cigarettes were harmful. In addition, it would have extended to products like cigars, which was opposed by the industry, as was regulation of premium cigars, which threatened Democrats in tobacco-friendly states like North Carolina and Florida.

One former Obama administration health official, who asked not to be identified because it could jeopardize his employment as a lobbyist, said the political risk for banning flavors seemed too high, given Republican control of Congress. The White House was worried about several Republican proposals that aimed to unravel the F.D.A.’s ability to regulate tobacco products.

“We were very nervous about what would happen if we did this,” the former official said. “Would the Obama ‘nanny state’ criticism come in to play? Not all Senate Democrats were strong champions of those things. There had to be give.”

The rule approved by the White House did set new requirements for the industry, including forbidding sales to minors and mandating the submission of ingredient lists by e-cigarette manufacturers.

In 2017, the vaping landscape shifted again with Mr. Trump’s appointment of Dr. Gottlieb, who had served on the board of Kure, a chain of vaping lounges. Although he divested from Kure when he became the F.D.A. commissioner, Dr. Gottlieb held on to the idea that vaping could help adults quit smoking.

Two months into his new job, he handed the e-cigarette industry the breathing room of a four-year extension to comply with the new rules as part of a broader package that appeared to straddle competing interests. He called for lowering nicotine in cigarettes to render them less addictive, while ensuring access to e-cigarettes and other alternatives for smokers trying to quit.

Then, in 2018, new federal survey data showed that teen vaping had jumped sharply in the past year, driven by the popularity of Juul, and that more than three million American high school students had tried e-cigarettes.

“It was just a horror show,” said Katy Talento, a former top health policy adviser to Mr. Trump on the Domestic Policy Council. After that, she said, “the calculus changed.”

In an interview, Dr. Gottlieb said he then began lobbying the White House and lawmakers to win support for an e-cigarette crackdown.

“I couldn’t outright ban the sale of e-cigarettes in convenience stores, because the law prohibited me from doing that,” he said. “And that’s where the kids were accessing the products.”

Last month, after Dr. Sharpless and Alex M. Azar II, the secretary of health and human services, told White House officials that new figures showed teen vaping had increased again, they said they would draft the proposed ban on most flavored e-cigarettes.

“We can’t allow people to get sick,” the president said, with his wife Melania at his side in the Oval Office. “And we can’t have our youth be so affected.”

Mr. Trump recently tweeted that he liked “the vaping option to cigarettes” but wanted to retain young young children from working with the items.

Some states and cities have stepped in. Massachusetts has halted sales of all vaping items for 4 months, and other states, such as Michigan, Rhode Island, Washington, Oregon and New York, have imposed flavor bans or taken methods to do so. And a number of big retailers, such as Walmart, Walgreens and other folks, have stated they would quit promoting e-cigarettes altogether.

Efforts to track the trigger of the lung illnesses have been hampered by the reality that THC-primarily based items largely fall into a regulatory vacuum, and relaxed laws in lots of states have enabled an illicit trade. Although marijuana is nevertheless illegal at the federal level, almost 3 dozen states permit medicinal use, and 11 states and the District of Columbia have totally legalized it.

The F.D.A.’s authority more than THC is viewed as a gray location of law. A handful of cannabis-derived drugs have been authorized, and the F.D.A. is speaking to other agencies about expanding its attain.

Almost 1,300 persons, disproportionately young, have been sickened from vaping THC, nicotine or each. At least 29 have died.

It typically requires a public well being crisis for the federal government to enact big adjust, stated Dr. Califf, the former F.D.A. commissioner.

“It has to get negative sufficient ahead of you can basically get down to what desires to get carried out,” he stated. “And I guess in a way this is an instance.”

Julie Creswell contributed reporting.