I don't think they "goaded" Donald Trump into anything. I think they were praying that Trump would agree to the early debate. My theory is those around Biden could see that he was getting worse by the day, and knew a debate in the fall would end in disaster. By getting him out there as early as they did, they were hoping he still had enough left to appear competent. Even a mediocre showing in the debate would have been hailed Democrats and the media as a "strong performance in which Biden was clearly the winner." They would have then said no further debates were necessary, and kept Biden under wraps until election day.
They had two operational plans, fingers crossed he wouldn't fall flat on his face (which he did) OR, if he fell flat on his face it would finally get Nancy and Chuck to pull him off the stage which they had been hesitant to do.