Former president Donald Trump has rejected the House Democrats' request for him to testify in the Senate's upcoming impeachment trial, according to his trial defense attorney Bruce Castor. 

Castor simply said "no," when asked by NBC News if Donald Trump would appear in the upper chamber for the trial. Lead impeachment manager Rep. Jamie Raskin wrote a letter earlier Thursday, asking Trump to testify under oath.

"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 said in a Breitbart report.

Raskin wrote that in light of disputing these factual allegations, he is inviting Donald Trump to give testimony under oath, either before or during the Senate impeachment trial, regarding his connection with the Jan. 6 siege on the U.S. Capitol. Raskin said if Trump refused to do so, it plainly establishes an adverse inference supporting his guilt.

Aside from Castor, Trump adviser Jason Miller also said that the former president would not testify in the trial, which the lawyer described as an "unconstitutional proceeding," according to The Guardian report. Trump's lawyers also dismissed the request and dubbed it as a public relations stunt.

Raskin added that if Trump refuses to appear, the impeachment manager will use his refusal against him in the trial, which is a similar argument brought by House Democrats in last year's impeachment trial. This was when Trump officials also ignored subpoenas.

However, the impeachment managers do not have the authority to subpoena witnesses now since the House already voted to impeach him. The Senate could vote to subpoena Trump or any other witnesses. But it is still unclear if the Senate would be willing to do so.

Related story: 45 Republican Senators Vote To Dismiss Trump Impeachment Trial

House Democrats' Request on Donald Trump's Appearance

House Democrats on Thursday asked Donald Trump to testify for his Senate impeachment trial, challenging him to address their charge that he incited a violent mob that breached Capitol.

Democrats will be able to use his refusal to testify against him as they argue that the former president has avoided responsibility for his actions, according to an Associated Press report.

The impeachment trial starts on Feb. 9 as Donald Trump becomes the first president to be impeached twice. Trump was charged with inciting an insurrection on Jan. 6 when his alleged supporters broke into the Capitol establishment to interrupt the electoral vote count.

The Capitol riot left five people dead. Trump had allegedly told his supporters before the riot to fight like hell to overturn his election loss.

Meanwhile, Democrats said a trial is needed to provide a final measure of accountability for the attack. If Donald Trump is found guilty, the Senate could hold a second vote to disqualify him from seeking office again.

Raskin's request included the words of Trump's own attorneys, who denied in a legal brief early this week that Trump did not incite the riot and asserted that he had also performed admirably in his role as president and doing at all times what he thought was in the best interest of the American people.

Read also: Only 8% of Republicans Support Trump Impeachment: Poll