The email chain could provide evidence for multiple, ongoing government investigations into whether there was collusion between the Kremlin and Trump's Republican presidential campaign. U.S. intelligence agencies have concluded that Moscow meddled in the 2016 U.S. presidential election to help elect Trump.
Moscow has denied any interference, and Trump has insisted his campaign did not collude with Russia.
In the exchange, Goldstone said the offer of possibly damaging information about Clinton was "part of Russia and its government's support for Mr. Trump."
Legal experts are divided on whether accepting campaign information from a foreign government is, by itself, against the law.
The meeting, though, could run afoul of federal election laws, which prohibit the solicitation or acceptance of campaign contributions from foreign nationals.
"We (now) have smoking gun evidence of collusion," said Paul Butler, a professor at Georgetown School of Law, and a former federal prosecutor. "That collusion becomes a crime under federal law if you solicit a contribution from a foreign national."
But if the meeting produced no information of value to the Trump campaign, it could be hard to prove a contribution was made.
"There's no opposition research actually transferred. So, I don't know that he's actually in any legal trouble at all," said Rick Tyler, a political analyst at Foundry Strategies
Still, the statute also specifically bans the solicitation of contributions from foreign nationals, regardless of whether they're paid.
"If you solicit a contribution from a foreign national, that's a federal crime," Butler said. "A contribution doesn't have to be cash money. It could also be some kind of material aid like opposition research. With this tweetstorm this morning, Trump Jr. exposed himself to federal criminal liability."
Regardless of the criminal liability, the disclosures add to the political liability the White House faces from the ongoing Russia investigations.
"This exudes shadiness because they had a Russian connection from the get-go," said Michael Allen, a managing director at Beacon Global Strategies, a security consultant. "They knew or should have known that this was a terrible idea to have met with this person."