U.S. President Donald Trump blasted the “human scum” who launched impeachment proceedings against him on Thursday during another session of dramatic testimony into his suspect deal-making with Ukraine.

Trump took to Twitter to blast the proceedings at the same time as Fiona Hill, a Russia expert and former White House adviser, and David Holmes, a senior staffer at the U.S. Embassy in Ukraine, gave testimony on Capitol Hill.

The 45th president lashed out at Adam Schiff, the Democrat leading the impeachment inquiry in Congress, and urged fellow Republicans to stiffen their resolve against what he termed abuses of

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