By admitting that Rubio had a bad moment, but emphasizing that Rubio recovered and had good second half of the debate. I'm not sure if there was a Luntz focus group tonight, but if there was, I wouldn't be surprised if Rubio's answers on what it means to be a conservative and abortion scored well with Republican primary voters.
I don't think anything can be salvaged between today and Tuesday. Tomorrow's pretty much a dead day in the campaign, leaving only Monday to really change message. I'd pivot to focus on Rubio's accomplishments in Washington and Tallahassee, if possible.
Luntz's focus groups have already been exposed as rigged for Rubio. I'm sure he'd have said he won the robot moment too.
In other words, let's dispel with this fiction that Frank Luntz doesn't know what he's doing. He knows exactly what he's doing.