Sen. John McCain (R-Ariz.) on Sunday said President Trump either has to retract his claim that former President Barack Obama wiretapped Trump Tower, or provide evidence of the allegations.

“President Trump has to provide the American people, not just the intelligence community, but the American people, with evidence that his predecessor, former president of the Unites States was guilty of breaking the law,” McCain told CNN’s “State of the Union.”

Trump last weekend accused Obama of wiretapping Trump Tower just before the November presidential election. The president did not provide evidence. Obama, through a spokesman, denied that he or any White House official ordered surveillance.

{mosads}The White House has called on Congress to include an investigation into any potential surveillance as part of its probe on Russia’s interference in the presidential election.

The House Intelligence Committee has asked the White House to provide any evidence of the allegations by Monday.

McCain said on Sunday that if Obama “violated the law” by ordering a wiretap, then “we’ve got a serious issue.”

“I have no reason to believe that the charge is true, but I also believe that the president of the Unites States could clear this up in a minute,” McCain said, adding that Trump could call the director of the CIA and the director of national intelligence for proof.