A Republican congressman said Friday that, without “pretty compelling proof,” President Donald Trump should apologize to former President Barack Obama for Trump’s unsubstantiated claim that Obama ordered surveillance on him during the 2016 campaign.

“I see no indication that that’s true,” Rep. Tom Cole (R-OK) told CNN’s Manu Raju of Trump’s charge. “And so it’s not a charge I would have ever made.”

“Frankly, unless you can produce some pretty compelling proof, then I think the President, you know, President Obama is owed an apology in that regard. If he didn’t do it, we shouldn’t be reckless in accusations that he did,” Cole told reporters.

Trump has offered no evidence for his claim, though he referenced news reports that used the word “wiretap,” a term he used, in an interview Wednesday.

White House press secretary Sean Spicer did the same on Thursday, including reading from a report accusing the British intelligence service of providing Obama with surveillance on Trump.

The U.S. government has since apologized for the claim against Britain’s GCHQ.