The memo represents an especially strong rebuke of the GOP-backed conspiracy theories, which media “must state clearly and unambiguously that they have been discredited and debunked by authoritative sources,” Bedingfield and Blinken said.

“To fail to make clear that the conspiracy theory and false accusations about Joe Biden have been comprehensively disproven, to artificially prop-up these egregious lies based on the 'principle' that if partisans make accusations, they have to be treated as legitimate regardless of the facts, is to make you an enabler of misinformation,” the memo warned reporters and media outlets.

Biden has insisted that neither he nor his son engaged in any wrongdoing.

Trump and Republican lawmakers have pushed to have Biden and his son testify at the impeachment trial, but Rep. Jerry Nadler, who’s serving as one of the impeachment managers, firmly rejected the idea during an interview on CBS’ “Face the Nation.”

“This whole controversy about whether there should be witnesses is really a question of does the Senate want to have a fair trial or are they part of the coverup of the president?” Nadler said. “Any Republican senator who says there should be no witnesses or even that witnesses should be negotiated is part of the coverup.”

Late last year, Trump became the third president in U.S. history to be impeached after blocking $400 million in aid to Ukraine as he pressured Ukrainian President Volodymyr Zelensky to open an investigation into Biden’s activities.

Opening arguments for Trump’s impeachment trial will begin Tuesday.