Donald Trump Jr.'s email bombshell is a development like no other in the Russia saga

A monthslong talking point of President Donald Trump, who often alleges the story of his campaign's possible collusion with Russia is a "hoax," unraveled on Tuesday.

And his son was the one pulling the thread.

Donald Trump Jr., the president's eldest son, tweeted an email chain on Tuesday dating back to June 2016 in which he entertained accepting damaging information on Hillary Clinton as part of the Russian government's support for his father's campaign.

"Good morning," Rob Goldstone, the music publicist for Russian pop star Emin Agalarov, wrote to Trump Jr. on June 3, 2016. "Emin just called and asked me to contact you with something very interesting.

"The crown prosecutor of Russia met with his father Aras [Agalarov] this morning and in their meeting offered to provide the Trump campaign with some official documents and information that would incriminate Hillary and her dealings with Russia and would be very useful to your father," he continued. "This is obviously very high level and sensitive information but is part of Russia and its government's support Mr. Trump - helped along by Aras and Emin."

If Trump Jr. was skeptical or wary, he did not indicate as much in his response.

"If it's what you say I love it especially later in the summer," he wrote. "Could we do a call first thing next week when I am back?"

The four-page email chain, which Trump Jr. forwarded on to his father's campaign manager, Paul Manafort, and son-in-law Jared Kushner, culminated in their meeting at Trump Tower on June 9 with Natalia Veselnitskaya - a lawyer described by Goldstone in his emails as a "Russian government attorney."

But Trump Jr., by his own admission, emerged from the meeting disappointed.

"She had no information to provide and wanted to talk about adoption policy and the Magnitsky Act," he said in a statement. "As Rob Goldstone just said today in the press, the entire meeting was the 'most inane nonsense I ever heard. And I was actually agitated by it.'"

The episode betrays what has become one of Trump's go-to rebuttals when confronted with a media report about his campaign's alleged ties to Moscow.

"The Russia-Trump collusion story is a total hoax," he tweeted on May 8. "When will this taxpayer funded charade end?"

The denials date back to late July 2016, when Trump first claimed that he has "nothing to do with Russia." His spokespeople followed his lead amid reports that Kremlin officials were in touch with the campaign, and that campaign surrogate-turned national security adviser Michael Flynn communicated with Russian ambassador Sergey Kislyak.

"There was no communication between the campaign and any foreign entity during the campaign," Hope Hicks, then Trump's communications director, said on November 11.

"Those conversations never happened," former campaign manager Kellyanne Conway said on December 18. "I hear people saying it like it's a fact on television. That is just not only inaccurate and false, but it's dangerous."

"I think to suggest that is to give credence to some of these bizarre rumors that have swirled around the candidacy," Vice President-elect Mike Pence told CBS on January 15 when asked if the campaign had communicated with Russians wanting to meddle in the election.

Flynn was ultimately forced to resign over his conversations with Kislyak, but the White House has maintained that the communication was diplomatic in nature and therefore not improper. Kushner's meetings in December with Kislyak and the CEO of a sanctioned Russian bank, Sergey Gorkov, have been similarly dismissed by the administration as efforts to improve Washington's relationship with Moscow.

Trump and his associates have been able to fend off accusations of collusion with Russia because most, if not all, of the concrete reporting on the campaign's contacts with Russians has focused on events following the election.

But the meeting with a Russian attorney just weeks after Trump secured the Republican nomination - for the specific purpose of obtaining dirt on Clinton that they were told came from the Russian government - contradicts months of denials from the White House.

It signals that the campaign was willing to accept Russian help, which leaves the administration exposed to conspiracy and collusion charges in a way no other Russia-related revelation has up to this point.

Andy Wright, a professor of constitutional law at Savannah Law School, said last month that if Americans entered into an agreement to assist illegal Russian influence operations, "it could create a conspiracy which is a federal crime."

Additionally, Wright said, American citizens colluding with a foreign power to illegally affect an election "could constitute aiding and abetting that foreign power's criminal campaign finance violation."

"Our national security clearance system relies on being able to vet foreign sources of leverage," Wright said. "Of course, the premise of kompromat is shame. Some of the president's defenders appear to be post-shame."