Graham: There will be 51 GOP votes to call Bidens, whistleblower

Sen. Lindsey GrahamLindsey Olin GrahamThis week: House to vote on legislation to make lynching a federal hate crime Congress set for clash over surveillance reforms Five things to know about emerging US, Taliban peace deal MORE (R-S.C.) predicted on Tuesday that if the Senate opens the door to calling new witnesses, Republicans will vote to subpoena President TrumpDonald John TrumpAdvisor: Sanders could beat Trump in Texas Bloomberg rips Sanders over Castro comments What coronavirus teaches us for preventing the next big bio threat MORE's top targets.

“I'll make a prediction: There will be 51 Republican votes to call Hunter Biden, Joe BidenJoe BidenBiden faces do-or-die primary in South Carolina Democrats view Sanders as having best shot to defeat Trump: poll Karl Rove: 'Long way to go' for Sanders to capture nomination: 'The field is splintered' MORE, the whistleblower and the DNC staffer at a minimum,” Graham told reporters.

His comments come as former national security adviser John BoltonJohn BoltonTrump directly sought to block publication of Bolton's book: WaPo 'Parasite' studio fires back after Trump criticism: 'He can't read' Trump swipes at 'little wise guy' Brad Pitt, Korean film 'Parasite' during rally MORE’s claim in his forthcoming memoir that President Trump tied Ukraine aid to the country opening up investigations into former Vice President Joe Biden and his son Hunter Biden.

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GOP leadership had hoped to end the trial with no witnesses, but Bolton's accusation, reported by The New York Times, has thrown the ability of the caucus to quickly end the trial into question. 

Conservatives are warning that if four Republican senators side with Democrats to call Bolton, then Trump's legal team should get as many witnesses. Since Democrats would not support calling the Bidens or the whistleblower, Republicans would have to provide the 51 votes from their 53 members. 

The Senate is expected to vote Friday on whether to call witnesses. If 51 senators support calling witnesses, that would open the door to both sides making motions for specific individuals. The Senate would then vote on those specific individuals. 

Democrats have said they want to subpoena four individuals, including Bolton and acting chief of staff Mick MulvaneyJohn (Mick) Michael MulvaneyWhite House preparing to ask Congress for funds to combat coronavirus: report Tucker Carlson calls out Mick Mulvaney on immigration remarks: 'Dishonest and stupid' Trump furious after officials allowed Americans with coronavirus to fly home with other passengers: report MORE.

Updated: 1:23 p.m.