Donald Trump is refusing to testify under oath at his second impeachment trial, which is set to get underway on Tuesday.
In a letter to Jamie Raskin, the House Democrats' lead impeachment manager, Mr Trump's lawyers branded the request a "publicity stunt" and claimed the trial was "unconstitutional".
"Your letter only confirms what is known to everyone: you cannot prove your allegations against the 45th President of the United States, who is now a private citizen," the letter states, in reference to the charge that Mr Trump incited the riot at the Capitol last month.
It is meanwhile being reported that the ex-president is planning a "revenge tour" to attack disloyal Republicans who voted for his impeachment in the House of Representatives in January.
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