"I don't think the transcripts should have been leaked," Sen. Ben Cardin told CNN's John Berman Friday on "New Day." "We've had reports on both ... the Australian call was well reported. So I don't think it was a surprise to read the transcripts."
"In regard to Mexico, there (were) new revelations," the Maryland lawmaker added. "Those transcripts should never have been released -- but they're not surprising."
According to a transcript published Thursday by The Washington Post, President Donald Trump boasted
about his election victory, pressured his Mexican counterpart to remain quiet about a border wall and called New Hampshire a "drug-infested den" in a phone call with Mexican President Enrique Peña Nieto.
The transcript of Trump's conversation with Mexico's leader was one of two phone calls revealed on Thursday, which provide a rare glimpse into the private conversations of a new US president testing his negotiating powers on foreign counterparts.
Trump insisted that Peña Nieto refrain from insisting publicly that Mexico will not pay for the wall's construction, which was one of Trump's major campaign promises.
"You cannot say anymore that the United States is going to pay for the wall," Trump said. "I am just going to say that we are working it out. Believe it or not, this is the least important thing that we are talking about, but politically this might be the most important talk about."
Asked to comment on the transcripts, Michael Anton, a spokesman for the National Security Council, said only that he "can't confirm or deny the authenticity of allegedly leaked classified documents."
On CNN, Cardin said he was not surprised to hear that Trump was not as aggressive on the border issue in private as he was when talking to his base.
"I think we all understand it," he said. "We know Mr. Trump is very sensitive about the wall. We know he has no support in the Congress to build a wall on our total border. It's not a surprise to hear what's in it. But that information should not have been leaked."
David Axelrod, a senior adviser to former President Barack Obama, tweeted that Trump's comments were "embarrassing," but agreed that leaking transcripts of diplomatic discussions doesn't bode well for the future.
"Transcripts of @POTUS calls w/leaders of Mexico; Australia were embarrassing. Yet the leaking of them feels like a terrible precedent," he tweeted Thursday.