Putin knows Biden is a coward and an incoherent mess in private conversation, but talks a big game to the press after the fact. Biden is full of shit and Putin knows it. Biden did everything he could to avoid debating his own political opponent up to and including getting his own pals to moderate the debate and change the rules to cut off Trump. There's not a chance in hell he would take Putin up on the offer even under the condition Putin had to do the whole debate in English, blindfolded.