Sen. Tim Kaine (D., Va.) told reporters on Tuesday that the Russia investigation is potentially moving into a "treason" investigation after reports surfaced of Donald Trump Jr.'s meeting with a Russian lawyer last summer.

In the wake of New York Times reports on Trump Jr. and other Trump campaign officials meeting with a Russian attorney who they believed had damaging information about Hillary Clinton, Kaine said the probe into obstruction of justice could evolve into something more serious.

"Nothing is proven yet, but we're now beyond obstruction of justice in terms of what's being investigated," Kaine said. "This is moving into perjury, false statements, and even into potentially treason."

Kaine was Clinton's running mate in the 2016 presidential election.

Kaine added, "To meet with an adversary to try to get information to hijack democracy. The investigation is now more than just obstruction of justice in investigation. It's more than just a perjury investigation. It's a treason investigation."

The New York Times reported Trump Jr. received an email that the material on Clinton he would get in the meeting was part of a Russian government effort to boost his father's campaign.

Trump Jr.'s explanations for the meeting have shifted, as he originally stated it was a discussion about Russian adoptions in the U.S.

After the Times first story on Sunday about the meeting, however, he expanded on his statement, saying he took the meeting believing that the woman had knowledge about Russian-connected individuals boosting the Democratic National Committee and Clinton.

The lawyer, Natalia Veselnitskaya, told NBC that she had no connection to the Kremlin and never had any damaging information on Clinton.

UPDATE: 11:02 A.M.: This article was updated with additional remarks by Kaine and more details on the New York Times stories about Clinton.