Lindsey Graham says Trump's impeachment 'invalid' without whistleblower testimony

Senate Judiciary Chairman Lindsey Graham on Sunday asserted that the impeachment inquiry into President Donald Trump is "invalid" unless the identity of the anonymous whistleblower whose complaint sparked House Democrats' probe, is revealed.

Graham, whose committee would be at the centre of Trump's trial in the Senate, also said in his Sunday interview with Fox News that the process would be "dead on arrival" in the Republican-controlled chamber if the whistleblower doesn't testify before Congress.

"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 and I also see the need for Hunter Biden to be called to adequately defend the President and if you don't do those two things it's a complete joke," said Graham, a Republican from South Carolina.

"It's impossible to bring this case forward in my view fairly without us knowing who the whistleblower is and having a chance to cross-examine them about any biases they may have. So if they don't call the whistleblower in the House, this thing is dead on arrival in the Senate," he continued.

Graham's remarks came a day after House Republicans and Democrats sparred over whether the whistleblower would provide testimony as part of the impeachment inquiry.

House Republicans had submitted to Democrats earlier Saturday a list of 15 witnesses they'd like to testify as part of the chamber's impeachment enquiry into Trump and Ukraine, seeking testimony from the whistleblower, former Vice President Joe Biden's son Hunter Biden and former US special envoy for Ukraine Kurt Volker, among others.

The whistleblower's complaint at the heart of the House's inquiry alleges that Trump pushed Ukraine to investigate Joe Biden, the former vice president's son and the 2016 election in order to help the President politically and that the White House took steps to cover it up. Trump has denied doing anything improper.

Trump has pushed an unproven accusation that then-Vice President Biden improperly tried to help his son by pressuring the Ukrainian government to fire the country's prosecutor general. Hunter Biden served on the board of the Ukrainian natural gas company at the time.

There is no evidence of wrongdoing by either Joe or Hunter Biden in Ukraine.