President Donald Trump called House Democrats' impeachment inquiry into him "a lynching" on Tuesday.

"So some day, if a Democrat becomes President and the Republicans win the House, even by a tiny margin, they can impeach the President, without due process or fairness or any legal rights," Trump tweeted. "All Republicans must remember what they are witnessing here - a lynching. But we will WIN!"

Trump's tweet invited swift backlash from prominent activists, politicians, and public figures who denounced it as inaccurate, ahistorical, and racially insensitive.

The president has outwardly expressed confidence that he'd be able to weather impeachment given the likelihood that he'd be acquitted by the Republican-controlled Senate.

But there may be some cracks in the red wall, as some Republican lawmakers say they could be open to removing Trump from office based on what new information the impeachment inquiry uncovers.

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President Donald Trump ramped up his rhetoric against House Democrats' impeachment inquiry on Tuesday, calling it "a lynching."

"So some day, if a Democrat becomes President and the Republicans win the House, even by a tiny margin, they can impeach the President, without due process or fairness or any legal rights," Trump tweeted. "All Republicans must remember what they are witnessing here - a lynching. But we will WIN!"

Trump's tweet invited swift backlash from prominent activists, politicians, and public figures who denounced it as inaccurate, ahistorical, and extremely racially insensitive. Historians describe lynchings — or the public, extrajudicial hangings of black Americans during Reconstruction and Jim Crow — as a form of domestic terrorism.

A 2015 report from the Equal Justice Initiative documented 4,075 lynchings of African-Americans throughout 12 southern segregated states between 1877 and 1950. The report also noted that the number is likely vastly undercounting.

"Lynchings were violent and public events that traumatized black people throughout the country and were largely tolerated by state and federal officials. This was not 'frontier justice' carried out by a few marginalized vigilantes or extremists," the report said. "Instead, many African Americans who were never accused of any crime were tortured and murdered in front of picnicking spectators."

Cracks are emerging in the 'red wall' protecting Trump from impeachment

The president has outwardly expressed confidence that he'd be able to weather impeachment given the likelihood he'd be acquitted by the Republican-controlled Senate.

But Trump has frustrated even his staunchest backers in recent days thanks to his abrupt decision to withdraw US troops from northeastern Syria and his announcement that next year's G7 summit would be held at the Trump National Doral in Miami. Trump hastily walked back the G7 decision after reports surfaced that Republican lawmakers refused to defend the perceived conflict of interest.

We've also seen some cracks in the red wall when it comes to impeachment. In recent days, two GOP senators indicated they might be wavering on their support for the president.

Read more: The White House is 'trying to put the toothpaste back in the tube' after Mick Mulvaney's disastrous press conference

Sen. Lindsey Graham. Sean Rayford/Getty Images

Sen. Lindsey Graham of South Carolina told Axios he could be open to impeaching the president if evidence emerged that Trump had engaged in a "quid pro quo" arrangement with Ukraine in an effort to get dirt on the 2020 Democratic presidential contender Joe Biden and his son Hunter Biden.

And Sen. Mitt Romney of Utah listed several reasons for impeaching Trump, including racist rhetoric, extramarital affairs, and abandonment of the US's Kurdish allies in Syria.

The president's tweet on Tuesday came with Bill Taylor, the US's top diplomat in Ukraine, preparing to testify before the three congressional committees conducting the impeachment inquiry.

Taylor has firsthand knowledge about efforts by two other diplomats — Gordon Sondland and Kurt Volker — to help Trump and his personal lawyer Rudy Giuliani push the Ukrainian government to launch politically motivated investigations that would benefit Trump at the same time the US was withholding military aid to Ukraine.

A career foreign-service officer, Taylor raised concerns multiple times in text messages with Volker and Sondland, at one point writing that it was "crazy" for the US to withhold security assistance to Ukraine in exchange for information that would personally benefit Trump's 2020 campaign. Overall, Trump officials have given mixed explanations about whether the aid was contingent on Ukraine's cooperation with Trump's political requests.

Read more: 3 big reasons Rudy Giuliani is the weakest link in Trump's inner circle as the Ukraine scandal widens

The impeachment inquiry is now a month old

House Speaker Nancy Pelosi announcing the formal impeachment inquiry into President Donald Trump on September 24. Associated Press

The public first learned of the shadow foreign policy campaign in Ukraine through a whistleblower complaint that a US intelligence official filed against the president in August. That complaint spurred House Democrats to launch a formal impeachment inquiry examining whether the president used his public office for private gain.

At the center of the complaint is a July 25 phone call Trump had with Ukrainian President Volodymyr Zelensky, during which Trump repeatedly pressured his Ukrainian counterpart to investigate the Bidens and help discredit the FBI's Russia investigation.

Trump ordered a hold on a nearly $400 million military-aid package to Ukraine days before the call. While he didn't explicitly mention the aid during his conversation with Zelensky, the US president reminded Zelensky how "we do a lot for Ukraine."

When Zelensky agreed and said his government would like to purchase Javelin missiles from the US, Trump immediately followed up by saying he would like Zelensky "to do us a favor, though," and investigate the Bidens and the Russia investigation. He also told Zelensky to work with Giuliani and Attorney General William Barr on the matter.

The president and his allies had long maintained that because he didn't directly mention the aid, there was no evidence of a quid pro quo. But Mick Mulvaney, the acting White House chief of staff, threw a wrench through that defense last week when he acknowledged during a press briefing that the aid was held up in part because Trump wanted Zelensky to investigate Democrats. He later tried to walk back the comments.

Grace Panetta contributed to this report.