The televised impeachment inquiry sessions come 46 years after America was transfixed by the Watergate hearings. Around three quarters of the US population watched at least some of the Watergate hearings on television.
A major difference this time will be social media, with Republicans and Democrats able to react instantly to developments.
Days before the hearings Republicans appeared increasingly fractured over how to defend the president.
Some Republican senators and members of Congress have stuck to Mr Trump’s description of his call with Mr Zelenskiy as “perfect,” and maintained there was no “quid pro quo” offered by the president.
Others have suggested there was an “appropriate quid pro quo”. And, some said his behaviour raised concerns but did not rise to the level of impeachment. There were also some who refused to discuss the matter at all, on the basis they would be jurors in an eventual Senate trial of Mr Trump.
Several Republican senators declared they would not even watch the televised hearings this week.
They included Lindsey Graham, a friend of Mr Trump, who called it a “sham”. He added: Its being driven by political people. I think this is a bunch of crap.”
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