Mr Trump's tweets, even deleted ones, are saved as part of the country's official record that goes to the National Archives and Records Administration. Former President Obama's Twitter account has also be archived.
Recently, senior White House aide Kellyanne Conway criticised the media for having “this obsession with covering everything he says on Twitter and very little of what of he does as President."
Mr Spicer said in his news briefing that Mr Trump is his own "most effective representative of his agenda."
Twitter "gives him the opportunity to speak to the American people...the same people critiquing him now," did so during the election, Mr Spicer noted.
Mr Spicer said it turned out to be "a very effective tool".
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