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"They essentially see themselves as engaged in a war to cripple by any means necessary a duly elected government," Barr said.

At the first impeachment hearing last Wednesday, Republicans repeatedly blasted Democrats for not calling an anonymous whistleblower to testify publicly or behind-closed doors. The whistleblower account of the July 25 call led to Democrats opening the inquiry.

Several witnesses testified last week that they were alarmed over the pressure tactics used against Ukraine, as well as the role of Trump's personal lawyer, Rudy Giuliani.

Eight more witnesses are due to testify in the second week of the televised hearings. They include Gordon Sondland, the U.S. ambassador to the European Union, whose direct interactions with Trump are likely to be a main focus in the investigation of whether the president made security aid to Ukraine contingent on it agreeing to dig up dirt on Biden, who is a leading contender for the Democratic nomination to take on Trump in 2020.