my take is that it's a prediction on perception, not the quality of the candidate. a lot of trump supporters were banking on Harris's inability to do or say anything off script, but thanks to the moderation those opportunities were scarce. with the cheating that we all know is happening, Trump needs a significant margin over Harris in order to beat the margin of fraud. since Harris looks competent if you squinted, that margin was not delivered via the debate like many of us thought it would.