Republican Sen. Lindsey Graham said he is certain that President Donald Trump will not be charged with obstruction of justice, given that the special prosecutor overseeing the Justice Department's investigation into Russia's election meddling has allowed former FBI Director James Comey to publicly testify before a Senate committee.

"Unless Mueller is a complete idiot, which he is not, he's concluded there's no obstruction of justice case because if he had concluded otherwise, Comey wouldn't be testifying," Graham, R-S.C., said of the Justice Department's special counsel, Robert Mueller, on "CBS This Morning" on Thursday.

"You wouldn't let his chief and only witness go through this process if you believe you really had a case to prosecute," Graham said. "And Mr. Mueller is a good prosecutor."

Graham first made that supposition on Wednesday night on Fox News hours before Comey was set to testify before the Senate intelligence committee that Trump had pressed him to drop investigation into former National Security Adviser Michael Flynn.

In response, House Intelligence committee ranking member Adam Schiff, D-Calif., on Thursday said it would be too soon to draw a conclusion.

"I would have to strongly disagree with my colleague Lindsey Graham," Schiff said Thursday, also on "CBS This Morning." "The fact that Bob Mueller is not worried about his testifying – I think that does not suggest anything about how Bob Mueller views the case."

"Indeed, I would be astonished if he had a view this early in the investigation. Rather, I think it shows confidence that Jim Comey will be consistent in his testimony before the Senate and in any later proceeding," Schiff continued. "But I wouldn't read any conclusion into that, one way or another."

Graham, in response, called Schiff's position "crazy."

"Nobody in their right mind who believed they had a case, would take their star witness and allow them to go before the nation and 20 senators," Graham said. "You just don't do it that way. So he's concluded, rightly, there's no obstruction of justice here. To think otherwise really is silly."

At the hearing Thursday morning, Comey said he believes Mueller was certainly investigating whether Trump should be charged with obstruction of justice.

Comey, asked by committee Chairman Richard Burr, R-N.C., if he felt Trump was trying to obstruct justice, Comey refused to draw his own conclusions.