President Donald Trump’s eldest son, Donald Trump Jr., was promised damaging information about Hillary Clinton before agreeing to meet with a Kremlin-connected Russian lawyer during the 2016 campaign, according to three advisers to the White House briefed on the meeting and two others with knowledge of it.

The meeting was also attended by his campaign chairman at the time, Paul Manafort, and his son-in-law, Jared Kushner. Manafort and Kushner only recently disclosed the meeting, though not its content, in confidential government documents described to The New York Times.

The Times reported the existence of the meeting on Saturday. But in subsequent interviews, the advisers and others revealed the motivation behind it.

The meeting — at Trump Tower on June 9, 2016, two weeks after Donald Trump clinched the Republican nomination — points to the central question in federal investigations of the Kremlin’s meddling in the presidential election: whether the Trump campaign colluded with the Russians. The accounts of the meeting represent the first public indication that at least some in the campaign were willing to accept Russian help.

And while Trump has been dogged by revelations of undisclosed meetings between his associates and the Russians, the episode at Trump Tower is the first such confirmed private meeting involving members of his inner circle during the campaign — as well as the first one known to have included his eldest son. It came at an inflection point in the campaign, when Trump Jr., who served as an adviser and a surrogate, was ascendant and Manafort was consolidating power.

It is unclear whether the Russian lawyer, Natalia Veselnitskaya, actually produced the promised compromising information about Clinton. But the people interviewed by The Times about the meeting said the expectation was that she would do so.

In a statement Sunday, Trump Jr. said he had met with the Russian lawyer at the request of an acquaintance. “After pleasantries were exchanged,” he said, “the woman stated that she had information that individuals connected to Russia were funding the Democratic National Committee and supporting Ms. Clinton. Her statements were vague, ambiguous and made no sense. No details or supporting information was provided or even offered. It quickly became clear that she had no meaningful information.”

He said she then turned the conversation to adoption of Russian children and the Magnitsky Act, a U.S. law that blacklists suspected Russian human rights abusers. The law so enraged President Vladimir Putin that he retaliated by halting U.S. adoptions of Russian children.

“It became clear to me that this was the true agenda all along and that the claims of potentially helpful information were a pretext for the meeting,” Trump Jr. said.

When he was first asked about the meeting Saturday, he said only that it was primarily about adoptions and mentioned nothing about Clinton.

Mark Corallo, a spokesman for the president’s lawyer, said Sunday that “the president was not aware of and did not attend the meeting.”

Lawyers and spokesmen for Kushner and Manafort did not immediately respond to requests for comment. In his statement, Trump Jr. said he asked Manafort and Kushner to attend, but did not tell them what the meeting was about.

U.S. intelligence agencies have concluded that Russian hackers and propagandists worked to tip the election toward Donald Trump, in part by stealing and then providing to WikiLeaks internal Democratic Party and Clinton campaign emails that were embarrassing to Clinton. WikiLeaks began releasing the material on July 22.

A special prosecutor and congressional committees are investigating the Trump campaign’s possible collusion with the Russians. Trump has disputed that, but the investigation has cast a shadow over his administration.

Trump has also equivocated on whether the Russians were solely responsible for the hacking. On Sunday, two days after his first meeting as president with Putin, Trump said in a Twitter post: “I strongly pressed President Putin twice about Russian meddling in our election. He vehemently denied it. I’ve already given my opinion ….. ” He also tweeted that they had “discussed forming an impenetrable Cyber Security unit so that election hacking, & many other negative things, will be guarded …”

On Sunday morning on Fox News, the White House chief of staff, Reince Priebus, described the Trump Tower meeting as a “big nothing burger.”

“Talking about issues of foreign policy, issues related to our place in the world, issues important to the American people is not unusual,” he said.

But Rep. Adam B. Schiff of California, the leading Democrat on the House Intelligence Committee, one of the panels investigating Russian election interference, said he wanted to question “everyone that was at that meeting.”

“There’s no reason for this Russian government advocate to be meeting with Paul Manafort or with Mr. Kushner or the president’s son if it wasn’t about the campaign and Russia policy,” Schiff said after the initial Times report.

Veselnitskaya, the Russian lawyer invited to the Trump Tower meeting, is best known for mounting a multipronged attack against the Magnitsky Act.

The adoption impasse is a frequently used talking point for opponents of the Magnitsky Act. Veselnitskaya’s campaign against the law has also included attempts to discredit the man after whom it was named, Sergei L. Magnitsky, a lawyer and auditor who died in mysterious circumstances in a Russian prison in 2009 after exposing one of the biggest corruption scandals during Putin’s rule.