Donald Trump Jr.'s meeting with a Russian lawyer who claimed to have damaging information on Hillary Clinton "borders on treason," an ethics lawyer under former President George W. Bush said Sunday.

"This was an effort to get opposition research on an opponent in an American political campaign from the Russians, who were known to be engaged in spying inside the United States," Richard Painter told MSNBC.

"We do not get our opposition research from spies, we do not collaborate with Russian spies, unless we want to be accused of treason."

Bush 43 WH ethics lawyer on NYT story/Donald Trump Jr. and Kushner meeting with Russian lawyer: This borders on treason via @MSNBC pic.twitter.com/Ceu5xLYgnB— Bradd Jaffy (@BraddJaffy) July 9, 2017

Painter said if this happened under the Bush administration, Trump Jr. and President Trump's son-in-law Jared Kushner, who was also present at the meeting, would be "in custody by now."

Trump's campaign chairman Paul Manafort also attended the meeting.

"This is unacceptable. This borders on treason, if it is not itself treason," he said.

The New York Times reported Sunday that Trump Jr. attended the June 2016 meeting with a Kremlin-linked lawyer Natalia Veselnitskaya after she promised to share compromising information on Clinton.

"After pleasantries were exchanged, the woman stated that she had information that individuals connected to Russia were funding the Democratic National Committee and supporting Ms. Clinton," Trump Jr. said in a statement to the Times.

"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."