Adam Schiff 'has not paid the price' for impeachment, Trump says in what appears to be veiled threat

House Democratic impeachment managers, from left, Jerrold Nadler, Hakeem Jeffries, Adam Schiff and Val Demings discuss the impeachment trial of Donald Trump. Photo / AP

US President Donald Trump escalated his attacks on Representative Adam Schiff on Sunday, issuing what appears to be a veiled threat against the California Democrat one day before Trump's team is expected to deliver the crux of its defense in the third presidential impeachment trial in US history.

"Shifty Adam Schiff is a CORRUPT POLITICIAN, and probably a very sick man," Trump tweeted Sunday morning. "He has not paid the price, yet, for what he has done to our Country!"

Schiff, chairman of the House Intelligence Committee, is the lead impeachment manager in the Senate trial.

Night falls on the Capitol in Washington last week, during the impeachment trial of President Donald Trump. Photo / AP

Schiff responded in an interview on NBC News' Meet the Press, saying he believes Trump's remarks were intended as a threat.

"This is a wrathful and vindictive president; I don't think there's any doubt about it," Schiff said in the interview. "And if you think there is, look at the president's tweets about me today, saying that I should 'pay a price.' "

"Do you take that as a threat?" host Chuck Todd asked.

"I think it's intended to be," Schiff replied.

Trump's targeting of Schiff comes as the president's attorneys are readying to mount an aggressive defense on Monday.

Democrats are arguing that Trump withheld military aid and an Oval Office meeting to pressure Ukraine's leaders into announcing investigations of his political rivals, including former vice president Joe Biden, who is a 2020 Democratic presidential candidate.

The House impeached Trump in December on charges of abuse of power and obstruction of Congress related to these allegations and his directive that his administration not cooperate with the House's investigation.

In a two-hour presentation on Saturday, members of Trump's legal team argued that the president had valid reasons for withholding the aid to Ukraine, and it sought to plant doubts about both the prosecutors' case and Schiff.

But in arguing their case, Trump's attorneys omitted facts, presented claims that lacked context or minimized evidence gathered by House investigators.

White House Press Secretary Stephanie Grisham said it was "ridiculous" for Schiff to claim that Trump was threatening him. In an appearance on Fox News Channel's Media Buzz, she accused the California Democrat of "grandstanding," although she acknowledged that she hadn't had an opportunity to ask Trump what he meant by the tweet."I think he means … (Schiff) hasn't yet paid the price with the voters," Grisham said.

She also echoed Trump's attack earlier Sunday on Schiff, saying, "I mean, it seems he's having a little bit of a mental issue when you sit on the floor for hours and hours and hours. He's obsessed with this president and trying to take him down."

Democrats contend that Trump has continued to publicly solicit foreign interference in US elections and that the integrity of the 2020 race is at risk. The president fired back Sunday by leveling the same accusation at his political opponents.

"The Impeachment Hoax is a massive election interference the likes of which has never been seen before," he said in a tweet.

Some Republicans on Sunday defended Trump's remarks about Schiff. In an interview on CNN's State of the Union James Lankford of Oklahoma said he was not troubled by Trump's declaration that Schiff "has not paid the price".

"I don't think it's a death threat. I don't think he's encouraging a death threat," Lankford said.

Host Jake Tapper responded by saying that "people who are supporters of the president have heard his rhetoric and then actually tried to bomb and kill politicians and the media".

This prompted Lankford to refer to the 2017 congressional baseball shooting that targeted Republicans and injured several people, including House Minority Whip Steve Scalise.

"So to be able to say the president's trying to be able to spur this on would be able to say Democrats were trying to spur on the killing" of Republicans, Lankford said.

House impeachment manager Zoe Lofgren said Trump really ought to get a grip and be a little more presidential. Photo / AP

Zoe Lofgren, who is also an impeachment manager, called Trump's tweet about Schiff "really unfortunate" and said the president has said things before "that seem threatening to people".

"He really ought to get a grip and be a little more presidential," she said on State of the Union.

In a tweet later Sunday morning, Trump also took aim at Todd, accusing the Meet the Press host of holding a "softball interview" with Schiff and "never even calling Shifty out on his fraudulent statement to Congress, where he made up ALL of the words of my conversation with the Ukrainian President!"

Both sides continue to spar over the question of whether the Senate trial will include witnesses. Some key Senate Republicans, already hesitant on the issue, became even more so over the weekend after Schiff referred to a CBS News report in which an anonymous Trump ally was quoted as having warned lawmakers, 'Vote against the president and your head will be on a pike.' "

Several of those GOP senators - including Lisa Murkowski of Alaska and Susan Collins of Maine - have criticised Schiff for referencing the report, maintaining that the White House has not threatened them to vote against calling witnesses.

Schiff on Sunday defended his remarks, arguing that they weren't personal and were intended simply to highlight the challenge for Republican senators in demonstrating "moral courage to stand up to this president".

"I want to acknowledge that, and I don't want to acknowledge it in a way that is offensive to them, but I do want to speak candidly about it," he said. "And if this weren't an issue, there wouldn't be an issue about calling witnesses. If we can't even get the senators to agree to call witnesses in a trial, it shows you just how difficult that moral courage is."

Another impeachment manager, Val Demings of Florida said on ABC News' This Week that she continues to hope that members of the Senate will vote to call witnesses. She noted that she has been in the Senate chamber with senators for "some pretty long days" over the past week and that many of them have been taking notes on the proceedings.

"I would expect them to do what they have taken an oath and sworn that they would do," Demings said. "I'm just not going to give up on the Senate, and I'm not going to draw any conclusions."

Some Republicans, meanwhile, took to the Sunday shows to voice skepticism of the need for the trial to include witnesses.

Tom Cotton of Arkansas argued that Democrats have presented plenty of information already, little of which he said he found compelling. "We don't need to prolong what's already taken five months of the American people's time," Cotton said on CBS News' Face the Nation.

On Meet the Press, Schiff also appeared to play down the significance of a potential Senate vote to acquit Trump, arguing that such a vote would be meaningless if no witnesses are allowed to be called.

"They don't really contest the president's scheme. ... They just tried to make the case that you don't need a fair trial here; you can make this go away," Schiff said of the president's legal team. "But look, if they're successful of depriving the country of a fair trial, there is no exoneration."

Harvard Law emeritus professor Alan Dershowitz, a member of Trump's impeachment team, claimed Sunday that impeaching Trump based on the charges brought by the House would be unconstitutional because in his view, the charges do not rise to the level of high crimes and misdemeanors.

"Much of what was presented by the Democrats were not impeachable offenses - they were campaign ads designed to try to show that you should vote for a different candidate," Dershowitz told "Fox News Sunday," adding: "That's fine. Let's put it up to the voters."

Dershowitz is expected to argue Monday on the Senate floor that the two articles represent "vague, open-ended criteria" rather than impeachable offenses. He also argues that the framers of the Constitution would agree with him, a claim that is disputed by Democrats and other legal scholars.