US President Donald Trump says the Democratic politician leading the impeachment case against him has "not paid the price, yet" for his actions, a statement the Democrat views as a threat.
Mr Trump's attack on Adam Schiff and other Democrats followed days of their arguments in his impeachment trial before the US Senate.
Mr Trump is facing charges he abused the power of his office by pressuring Ukraine to investigate a political rival, and then tried to obstruct an investigation by Congress.
"Shifty Adam Schiff is a CORRUPT POLITICIAN, and probably a very sick man. He has not paid the price, yet, for what he has done to our Country!" he said on Twitter.
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Asked on NBC's Meet the Press if he took the Republican president's social media post as a threat, Mr Schiff said, "I think it's intended to be".
As lead impeachment manager, Mr Schiff, chairman of the House Intelligence Committee, played a central role in Democrats' efforts to paint the president’s behaviour as dangerous to democracy in America and around the world.
Mr Trump is likely to be acquitted at his impeachment trial in the Republican-led Senate, where a two-thirds majority is needed to find him guilty.
Mr Trump's team of lawyers began their defence on Saturday, arguing Democrats' efforts to remove the president from office would set a "very, very dangerous" precedent in an election year.
