Rep. Adam Schiff on Saturday made clear that the whistleblower would not be called to testify. On Sunday, Sen. Lindsey Graham said that if the House goes that route and opts to impeach, "this thing is dead on arrival in the Senate." He also wants to see the anonymity gone. In an appearance on Fox News' Sunday Morning Futures , he said "I consider any impeachment in the House that doesn't allow us to know who the whistleblower is to be invalid because without the whistleblower complaint, we wouldn't be talking about any of this." CNN reports it's unclear what he meant by "invalid."
Fox News explains Democrats' counterargument: that the whistleblower's testimony is "redundant" because witness testimony provided to date has already supplied more details on President Trump's July 25 phone call with Ukrainian President Volodymyr Zelensky than the whistleblower would be able to provide. (Read more Trump impeachment stories.)