Sen. John McCain (R-AZ) said Sunday that President Donald Trump should either provide proof for his claims that President Barack Obama “wire tapped” his phones at Trump Tower or retract those unsubstantiated allegations.

“I think the President has one of two choices: either retract or to provide the information that the American people deserve,” McCain said on CNN’s “State of the Union.”

On Monday, McCain told reporters that Congress should not investigate Trump’s claims unless there’s reason to believe that his allegations may be true.

“If there’s no basis for it, then there’s no reason for an investigation,” McCain said. “It’s his obligation to tell the American people why he made the allegation that he did.”

He called Trump’s accusations “unprecedented” and said he has never “seen anything like this.”

“President Trump has to provide the American people, not just the intelligence committee but the American people, with evidence that his predecessor, a former president of the United States, was guilty of breaking the law,” McCain said on Sunday. “Because our director of national intelligence, Gen. Clapper, testified that there was absolutely no truth to that allegation.”

The President has to “provide the American people with evidence,” says @SenJohnMcCain of Trump’s wiretapping claim https://t.co/Le7AlmBLqJ — CNN Politics (@CNNPolitics) March 12, 2017

House Intelligence Committee Chair Devin Nunes (R-CA) said on Tuesday that he has not seen any evidence for Trump’s unsubstantiated claims and suggested that reporters not take Trump’s comments “literally.”

Nunes nevertheless announced last week that his committee will “make inquiries” into Trump’s allegations.