Updated at 4:22 p.m. ET

Former President Donald Trump will not testify in the Senate impeachment trial, due to begin next week, Jason Miller, a senior adviser to Trump, tells NPR's Domenico Montanaro.

"The president will not testify in an unconstitutional proceeding," Miller said.

In a Thursday letter, Trump attorneys Bruce Castor and David Schoen called the request a "public relations stunt."

They are responding to a request from the lead House impeachment manager, who invited Trump to testify under oath in the Senate trial on the article of impeachment that says Trump incited the insurrection at the Capitol on Jan. 6.

"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," they wrote.

Earlier Thursday, Democratic Rep. Jamie Raskin wrote to Trump, inviting the former president to testify under oath in the trial.

"Two days ago, you filed an Answer in which you denied many factual allegations set forth in the article of impeachment. You have thus attempted to put critical facts at issue notwithstanding the clear and overwhelming evidence of your constitutional offense," Raskin wrote in the letter.

"In light of your disputing these factual allegations, I write to invite you to provide testimony under oath, either before or during the Senate impeachment trial, concerning your conduct on January 6, 2021. We would propose that you provide your testimony (of course including cross-examination) as early as Monday, February 8, 2021, and not later than Thursday, February 11, 2021. We would be pleased to arrange such testimony at a mutually convenient time and place."

On Tuesday, House managers filed a brief laying out their argument — that Trump whipped the crowd "into a frenzy" then aimed the protesters "like a loaded cannon" at the U.S. Capitol.

Trump's legal team then filed a response to the managers' brief, largely ignoring the factual assertions they laid out and arguing Trump did not incite the rioters.

Five people died as a result of the riot at the Capitol by pro-Trump extremists who had been egged on by Republicans to contest the legal outcome of the 2020 presidential election. Two additional officers who responded to the melee have died by suicide in the weeks since.

Trump, specifically, is accused of having incited the mob to storm the Capitol, particularly in a speech earlier in the day in which he told the crowd to walk to the Capitol in protest of the election results.

"You'll never take back our country with weakness," he told the crowd.

The trial is set to begin Tuesday.

This is Trump's second impeachment. He declined to participate in the first impeachment proceedings, which centered on whether he pressured the Ukrainian president to investigate Trump's political rivals.

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