As the second full day of President Trump's Senate impeachment trial opened Wednesday, Sen. Ben Cardin, D-Md., told “America’s Newsroom” that he was “open to listening to the president’s lawyers on any witness that they believe is helpful to present the president’s case."

Sen. Cardin made the comment in reaction to a Washington Post report that suggested some Democrats may be willing to agree to allow Hunter Biden to testify in exchange for Republican consent to allow former national security adviser John Bolton to appear.

“I don’t want to do a swap because I think that’s not the way we conduct a trial,” Cardin said. “You don’t do that type of trading. We want to hear from witnesses that either the managers think are important, or the president’s lawyers think are important for their defense but they must be relevant to the matters before us and they should be able to make that argument to the United States Senate.”

House Judiciary Committee Chairman Rep. Jerry Nadler, D-N.Y., one of the House impeachment managers, dismissed on Sunday any notion that Democrats would be willing to negotiate on witnesses, adding that Republicans who want to block or negotiate what witnesses testify are “part of the cover-up.”

CHIEF JUSTICE ROBERTS ADMONISHES BOTH SIDES AT SENATE IMPEACHMENT TRIAL, AFTER MARATHON SESSION ERUPTS INTO SHOUTING MATCH

House Intelligence Committee Chairman Adam Schiff, D-Calif., also dismissed the idea of a witness swap deal between the two parties.

“This isn't like fantasy football here," Schiff said. "We’re not making trades, or we shouldn't be."

“We’ll trade you one completely irrelevant immaterial witness that allows us to smear the president’s opponent in exchange for ones that are really relevant that you should hear," Schiff added. "Is that a fair trial?"

“I do think the president’s lawyers should have the opportunity to suggest witnesses that they believe are important for the president’s defense and they should be able to make the argument of relevancy, if they can,” Cardin told Fox News Wednesday. “We should hear those witnesses.”

“Clearly the witnesses that were brought forward by Senator [Chuck] Schumer had relevant information and should be called before the United States Senate. But we’re open, I’m open, to listening to the president’s lawyers on any witness that they believe is helpful to present the president’s case.”

SCHUMER SAYS IMPEACHMENT TRIAL STARTING UNDER 'CLOUD OF UNFAIRNESS'

Speaking at a news conference in Davos, Switzerland Wednesday, Trump said Bolton‘s potential testimony could pose "a national security problem.”

“He knows some of my thoughts,” he continued. “He knows what I think about leaders. What happens if he reveals what I think about a certain leader and it’s not very positive and I have to deal on behalf of the country?”

In response to the president’s statements Cardin said, “I don’t believe it’s up to the president initially as to who the Senate wants to call as far as relevant witnesses.

“As we get to his testimony, if there are issues that we have to resolve, we’ll resolve those issues,” he continued. “But quite frankly, as was pointed out in yesterday’s discussion, the executive immunity is not absolute. The courts upheld that it cannot be used to prevent the carrying out of our responsibilities, including now the oversight and impeachment proceedings. So there are limits to the use, but we would have to consider those matters.”

CLICK HERE TO GET THE FOX NEWS APP

“It doesn’t mean that we shouldn’t call Mr. Bolton," Cardin added. "He has critical information. There was a conversation that took place that’s been quoted frequently about how Mr. Bolton thought there was a quid pro quo, it’d be good to hear from him in that regard.”

Fox News’ Marisa Schultz and Andrew O’Reilly contributed to this report.