Sen. Ron Johnson, R-Wis., walked back comments that questioned whether Sen. John McCain's, R-Az., brain tumor affected his judgment when he voted against Obamacare repeal.

"I have the greatest respect for John McCain," Johnson said on CNN on Thursday. "He is not impaired in any way, shape, or form."

Johnson suggested on a local radio station Wednesday McCain's brain tumor, which was recently diagnosed, may have played a role in his surprise no vote on a "skinny" Obamacare repeal bill. The vote doomed the effort to pass the bill and start talks with the House for a new repeal bill.

"I'm not going to speak for John McCain — he has a brain tumor right now, that vote occurred at 1:30 in the morning, some of that might have factored in," Johnson said on the radio show "Chicago's Morning Answer."

McCain's office quickly responded that McCain has been "very open and clear about the reasons for his vote."

Johnson said on CNN he was not trying to criticize his colleague, but he was "trying to defend his position and express my sympathy for his health condition.

Johnson said he hopes to talk to McCain Thursday.