In its 231-year history, the Senate has completed 15 impeachment trials, and despite what President Trump's allies would have you believe, senators have heard witness testimony in every single case.
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In fact, not only has there been witness testimony at every single impeachment trial that the Senate has ever completed, but the Senate has often sought additional testimony from witnesses who did not testify in the House. 
Statements like these, in other words, have no basis in actual Senate precedent.
In just the last three impeachment trials the Senate has conducted, it has sought testimony from more than two dozen witnesses who did not testify before the House
In just the last three impeachment trials the Senate has conducted, it has sought testimony from more than two dozen witnesses who did not testify before the House
