David Chipman’s confirmation odyssey began with a short congratulatory buzz from Attorney General Merrick B. Garland in April and ended, he said, with a long, rueful call from the presidential adviser Steve Ricchetti admitting the White House had fallen “short.”

Mr. Chipman, a brash gun control activist whose nomination to head the Bureau of Alcohol, Tobacco, Firearms and Explosives imploded this month, said he had no other contact with the White House, which often left him feeling alone, on “an island,” when pro-gun groups attacked him.

Instead, the West Wing strategy focused on selling Mr. Chipman to Senator Joe Manchin III of West Virginia, the centrist Democrat and perpetual kingmaker in an evenly divided Senate, only to lose the support of Senator Angus King, an independent from Maine, which left Democrats at least one vote short of the 50 needed for confirmation.

“Either this was impossible to win, or the strategy failed,” Mr. Chipman told The New York Times in his first public comments since President Biden withdrew the nomination, conceding he could not get the votes. “This was a failure.”

Mr. Chipman’s defeat represented a major victory for the gun lobby and a huge loss for gun control groups, who saw appointment of a strong director for the bureau as the most important move Mr. Biden could make as Republicans block legislative action. It was a reminder of Mr. Biden’s struggles, eight months into his presidency, to fulfill big promises he has made to progressives on voting rights, immigration and guns.

In a far-ranging interview, Mr. Chipman, who served as an agent at the bureau for 25 years before becoming one of the country’s most prominent gun control activists, praised the White House for what he jokingly called the “gangster move” of nominating someone like him in the first place.

But he questioned the administration’s willingness to execute a coordinated strategy to get him through the Senate and expressed concern about its next moves. He said he found it “unusual” that he spoke to no one at the White House from the moment he was nominated.

“In the back of my mind, I always thought that there would be a Plan B, but so far there hasn’t been,” Mr. Chipman said.

White House officials pushed back on the suggestion that they are stalled, saying they are considering several possible nominees and pointing to new gun control, community engagement and anti-crime initiatives Mr. Biden outlined earlier this year.

“We know this work is going to be difficult — especially with Republicans on Capitol Hill moving in lock-step with the gun industry — but the president is absolutely committed to pushing both legislation and personnel to combat gun violence,” said Michael Gwin, a spokesman for Mr. Biden.

Mr. Chipman, 55, said he was speaking out now in hopes of encouraging Mr. Biden’s team to focus on reforming and energizing the long-neglected agency, which has been handcuffed by decades of legislative attacks from the National Rifle Association and other pro-gun groups.

He prefers to do so from the outside, rejecting a recent offer to serve in the Justice Department. He has returned to his position as an adviser to the organization founded by former Representative Gabrielle Giffords, a survivor of gun violence he described as having more courage than anyone in Washington.

Mr. Chipman placed most of the blame for his defeat on the gun lobby, in particular the National Shooting Sports Foundation, an industry trade group that lobbied Mr. King and others.

And he singled out Lawrence G. Keane, a top executive at the group, for posting a picture on its website showing a federal agent — falsely identified in a tabloid article as a young Mr. Chipman — standing in the smoldering debris of the Branch Davidian compound in 1993, which he said prompted a spate of online threats.

“Larry Keane put up a photo of me that he knew was false, trying to get me killed,” said Mr. Chipman, who arrived in Waco, Texas, to assist in the investigation long after the A.T.F. had begun an assault that eventually resulted in the deaths of 82 civilians and four federal agents.

Mr. Keane, in a phone interview, called the accusation “categorically false,” adding that “the moment we found out that it was in fact not him, we pulled it from our website. If I had known it wasn’t him, we would never have used the photograph.”

He acknowledged that Mr. Chipman was the subject of death threats, which he called “extremely unfortunate and uncalled-for.” But he said Mr. Biden never should have nominated someone as belligerent to gun owners, manufacturers and dealers as Mr. Chipman.

There was, however, one point both men agreed on: The White House, along with Mr. Chipman’s small support team at the Justice Department, did not do nearly enough to knock down that story or other accusations against him that circulated widely in conservative media.

Mr. Chipman lauded the dedication of the Justice Department team, but said his attempts to get them to send reporters documents debunking the Waco claim failed — and he finally had to give journalists the information himself after concluding “no one’s defending me.”

Administration officials, speaking on condition of anonymity because they were not authorized to speak publicly about the matter, said that they quietly countered negative stories about Mr. Chipman, but believed the under-the-radar media strategy was the wisest course.

They said the problem was not Waco, but Mr. King, an independent who caucuses with Democrats, who blindsided them by expressing opposition to Mr. Chipman just as the nomination was headed to a floor vote in late June.

A person close to Mr. King said his position should not have come as a surprise to anyone. He had already told administration officials he objected to their sales pitch — that the A.T.F., an agency he viewed as a neutral regulator, would be the focal point of gun policy under an activist director like Mr. Chipman.

Mr. Chipman got that message in person in July when Mr. King summoned him to his office.

When he arrived, Mr. King told the nominee that Mr. Chipman’s father — a King supporter who lives in Maine — had sent him a letter urging him to vote for his son.

“At least likes you,” Mr. King quipped.

Then the senator, who had been the subject of an intense lobbying effort by pro-gun groups in his home state, laid out his grievances. According to Mr. Chipman, the senator told him that “my friends who are gun dealers in Maine” objected to the nomination.

Mr. Chipman, who had vowed to intensify inspections of federally licensed gun dealers if confirmed, did not give ground — and polite calls from Mr. Biden, Ms. Giffords and Thomas Brandon, a former acting director of the agency, over the next few weeks did nothing to budge the senator.

By early September, the White House bowed to the inevitable. Mr. Ricchetti called Mr. Chipman, and spent about 20 minutes expressing regret at all he had been through, as the nominee stood near a field of sunflowers he was visiting with his wife.

Last week, Mr. King explained his position in a letter to constituents, saying Mr. Chipman could not be “a fair and objective regulator” because his association with gun safety groups meant he could not be “evenhanded” with gun dealers.

Mr. Chipman drew another conclusion from the meeting: that Mr. King had been “captured” by the gun lobby, and that his own defeat was a reflection of its enduring power.

“I left his office thinking, ‘Does he really believe that people who regulate industries can only get those jobs if they’re friends with the industry?’” Mr. Chipman said. “He said the quiet part out loud.”