President Donald Trump arrives at a campaign rally in Battle Creek, Mich., Wednesday, Dec. 18, 2019. (AP Photo/Paul Sancya)
FILE - President Donald Trump arrives at a campaign rally in Battle Creek, Mich., Dec. 18, 2019.

U.S. President Donald Trump continued to lash out at Democratic lawmakers over his impeachment Thursday as a legislative standoff continues over a Senate impeachment trial.

"The Radical Left, Do Nothing Democrats said they wanted to RUSH everything through to the Senate because 'President Trump is a threat to National Security' (they are vicious, will say anything!), but now they don’t want to go fast anymore, they want to go very slowly. Liars!," Trump wrote on Twitter.

On a near straight party line vote, the Democrat-controlled House of Representatives approved two articles of impeachment against Trump last Wednesday, making him only the third U.S. president to be impeached in the country's 243-year history. He is accused of abusing the power of the presidency to benefit himself politically and then obstructing congressional efforts to investigate his actions.

FILE - House Speaker Nancy Pelosi of Calif., readies to strike the gavel as she announces the passage of article II of impeachment against President Donald Trump, Dec. 18, 2019, on Capitol Hill in Washington.

House Speaker Nancy  Pelosi  has indefinitely postponed the sending of the articles of impeachment to Republican-controlled Senate so a trial can begin.  She says she will not act until the Senate agrees on rules governing the process.

Senate Majority Leader Mitch McConnell of Ky., speaks with reporters on Capitol Hill in Washington, Dec. 19, 2019.

Senate Majority Leader Mitch McConnell has softened his previous strong objection to demands from Democratic leader Chuck Schumer to hear testimony from four officials, including former National Security Advisor John Bolton and acting White House Chief of Staff Mick Mulvaney, during a Senate impeachment trial.

McConnell now says Republicans have not ruled out calling witnesses in Trump's impeachment trial.

"We haven't ruled out witnesses," McConnell told Fox & Friends Monday. "We've said, 'Let's handle this case just like we did with (former) President (Bill) Clinton.' Fair is fair."

Sen. Lisa Murkowski, R-Alaska, speaks in Washington, Dec. 11, 2018.

But Alaska Senator Lisa Murkowski, a moderate Republican, said she is disturbed to have heard McConnell say there would be "total coordination" between the White House and the Republican-controlled Senate in the way the trial would be conducted.

Murkowski told television station KTUU earlier this week that there must be a distance between the two bodies.

"To me, it means that we have to take that step back from being hand in glove with the defense. And so I heard what leader McConnell had said. I happened to think that that has further confused the process," she said.

Murkowski said she is undecided how she would vote in a Senate trial.

Trump's impeachment stems from a July call with Ukraine President Volodymyr Zelenskiy in which Trump asked for an investigation into former Democratic Vice President Joe Biden, a leading Democratic challenger to Trump in the 2020 presidential election.

Ukrainian President Volodymyr Zelenskiy speaks in Kyiv, Dec. 4, 2019.

Trump has insisted he did nothing wrong in his push to get Ukraine to investigate Biden and son Hunter Biden's lucrative work for a Ukrainian natural gas company. Trump had also called for a probe into a debunked theory that Ukraine meddled in the 2016 election.

Trump made the appeal for the Biden investigations at a time when he was temporarily withholding $391 million in military aid Kyiv wanted to help fight pro-Russian separatists in eastern Ukraine.

Trump eventually released the money without Zelenskiy launching the Biden investigations. Republicans say that is  proof Trump had not engaged in a reciprocal quid pro quo deal, meaning the military aid in exchange for the Biden probe.

Trump has on countless occasions described his late July call with Zelenskiy as "perfect," when he asked Zelenskiy to "do us a favor," to investigate the Bidens and Ukraine's purported role in the 2016 election. As the impeachment controversy mounted, Trump has subsequently claimed the "us" in his request to Zelenskiy referred not to him personally but to the United States.