The White House had recently said that the President used the word "wiretapped" in quotes, referring to the Obama administration broadly and not accusing his predecessor of personal involvement in wiretapping.
Senate Select Committee on Intelligence Chairman Richard Burr, R-N.C., and Vice Chairman Mark Warner, D-Va., issued the statement only hours after Trump told Fox News' Tucker Carlson that he would be providing evidence of his claims "very soon".
McCain was one of several top lawmakers in Congress to call on Trump to provide evidence of his unsubstantiated claim.
Obama's director of national intelligence, James Clapper, has said that nothing matching Trump's claims had taken place, but that has not quelled speculation that Trump's communications were monitored by the Obama administration.
The president is sticking to his guns.
"Wiretapping is pretty old-fashioned stuff", Trump said in an interview with Fox News Wednesday.
"You can surveil someone through their phones, certainly through their television sets - any number of ways", she continued before suggesting that there are even household appliances like "microwaves that turn into cameras". If you are, clearly the president is wrong.
On Wednesday the leaders of the House Intelligence Committee said they have yet to see any evidence of wiretapping, and House Speaker Paul Ryan insisted that "no such wiretap existed".
And when WikiLeaks posted new documents claiming to expose surveillance tactics available to the intelligence community, the White House steadfastly refused to confirm their validity, in keeping with long-standing U.S. policy about keeping spying operations secret.
Spicer all but screamed at Jonathan Karl, ABC News' chief White House correspondent, demanding, "Where was your passion and where was your concern when they all said that there was no connection to Russian Federation?"
Trump was also asked about the wiretap claims, and he gave a somewhat cryptic answer in response.
GCHQ has angrily denied helping former president Barack Obama to spy on Donald Trump. "I don't think there was an actual tap of Trump Tower".
Graham, for his part, said Wednesday the Senate would refuse to confirm Trump's deputy attorney general, Rod Rosenstein, if the Federal Bureau of Investigation did not disclose whether it had any evidence of wiretaps against Trump. I think the rest is created to downplay, minimize, or obfuscate the fact that the president said something that is patently untrue.