Lead impeachment manager Adam Schiff balked at the accusation that he is afraid of being called by President Trump's defense team as a fact witness for the Senate impeachment trial.

"If we're talking about a fair trial, if the senators are going to give content to their oath to be impartial administrators of justice, they can't say well, we're going to allow the president to trade witnesses that don't shed any light on the facts but would allow him to once again smear his opponent," Schiff said Sunday on NBC's Meet the Press.

Republicans have named Schiff as someone they would like to testify, as well as the intelligence community whistleblower whose report sparked Trump's impeachment and former Vice President Joe Biden's son Hunter, whom Trump sought investigations into. Schiff said these people were not relevant to the question before the Senate jury.

"If they're irrelevant, what are you afraid of?" moderator Chuck Todd asked the California Democrat.

"It's not a question of what I'm afraid of. I'm not afraid of anything," Schiff responded. "The question is, should the trial be used as a vehicle to smear [Trump's] opponent?"

The White House defense team spent the first day of its opening arguments Saturday calling Schiff's credibility into question and arguing that the president was acting out of legitimate concern about corruption in Ukraine when he asked the country's leader to investigate Biden.

Vital military aid to the country was briefly withheld while close associates of Trump worked to convince Ukrainian leadership to investigate charges of corruption against the former vice president's son.

Leading Republicans defending Trump have floated the idea of "witness reciprocity." Such a strategy would allow House impeachment managers to call additional witnesses they are seeking to hear from during a Senate trial while allowing Trump's team to do the same.

The same whistleblower who filed a complaint about the president's phone call with Ukraine also contacted Schiff's congressional office before reporting his concern to his superiors. Therefore, Schiff is a fact witness in the impeachment trial, some Republicans have argued, and so is Hunter Biden.

"Hunter Biden can't tell us anything about the withholding of the military funding," Schiff countered. "It's a false choice to say, well if the House gets to call witnesses, doesn't the president? Yes, we both get to call witnesses. We both get to call relevant ones."

