What you need to know:
- Trump is ending 2019 as the third president in US history to be impeached after pressuring Ukraine to investigate Joe Biden, a rival in his 2020 reelection bid.
- Democrats have also angrily berated the Republicans' apparent strategy of allowing no live witnesses or new documentary evidence at the trial.
Donald Trump faced calls from his own party to show more restraint on Twitter amid a storm of outrage Sunday over the president revealing the name of a man widely thought to be the whistleblower who triggered his impeachment.
Criticism has been growing since Trump retweeted an attack that included the name of the reported CIA staffer at the heart of the Ukraine scandal -- an act that could violate the whistleblower's guaranteed anonymity under the law.
"If the president would tweet a little bit less, it wouldn't cause brain damage. But the president does not have to take my advice, nor do I expect him to," Republican Senator John Kennedy, a key Trump ally, told "Fox News Sunday."
Trump is ending 2019 as the third president in US history to be impeached after pressuring Ukraine to investigate Joe Biden, a rival in his 2020 reelection bid.
The historic rebuke by the Democratic-controlled House of Representatives for abuse of office and obstruction of Congress is unlikely to pass the Republican-controlled Senate in a trial expected to begin in January.
But Trump, who is reportedly eager to celebrate his acquittal, has appeared increasingly frustrated that no date has been set for the trial amid a partisan standoff over its rules.
The president spent much of Friday amplifying pro-Trump and anti-Democrat tweets from suspicious-looking Twitter accounts at the start of what would become a weekend-long rant against the impeachment process.
The incendiary whistleblower retweet was no longer visible in the president's timeline by Saturday morning, although it was not clear who had removed it.
Political action group The Democratic Coalition tweeted Sunday that "while Trump has repeatedly backed efforts to unmask the whistleblower, his retweet marks the first time he has directly sent the alleged name to his 68 million followers."
Noah Bookbinder, who heads Citizens for Responsibility and Ethics in Washington (CREW), posted that "the president using his power and position to expose and implicitly threaten the Ukraine whistleblower is -- like so much else he has done -- utterly beyond the pale."
House Republican whip Steve Scalise attempted a defense of Trump's repeated demands for a Senate appearance from the whistleblower -- purportedly an intelligence analyst who said Trump linked US aid to Ukraine to his demand for the Biden investigation.
"Look, the whistleblower should have testified a long time ago," Scalise told Fox.
Democratic House Speaker Nancy Pelosi is holding on to the articles of impeachment that the House passed on December 18 -- meaning no Senate trial can begin.
She has berated Senate Republican leader Mitch McConnell -- who will take an oath of impartiality as a juror in the trial -- for publicly acknowledging his "total coordination" with the White House.
Democrats have also angrily berated the Republicans' apparent strategy of allowing no live witnesses or new documentary evidence at the trial.
Democrats want to hear testimony from several key past or present administration figures -- including former national security advisor John Bolton and Secretary of State Mike Pompeo -- who refused to testify to the House after Trump told them not to cooperate.
Republicans in turn want to hear from the whistleblower as well as former Vice President Biden and his son Hunter as they pursue a widely discredited claim that the elder Biden, while in office, sought to protect his son from a corruption inquiry in Ukraine.
"The Senate will have a fair trial and you'll see an acquittal," Scalise told Fox.
A prominent Democratic senator, Chris Van Hollen, on Sunday rejected speculation about an extended impeachment standoff.
Referring to Pelosi, he told ABC, "I think she's been very clear there will be a trial. And so, yes, she will be sending over the articles of impeachment."
But Van Hollen, who heads the Democratic Congressional Campaign Committee, warned that any Senate trial that barred both sides from calling witnesses or providing new documents would amount to a "sham" and a "rigged trial."