Seems a bit of a shallow way of picking someone. You don't want them because they seem weak when talking - so you're ignoring anything about their personality or beliefs, right?
Personally I'd rather go by their beliefs, record and actions. And on that score, well, it's a no-brainer.... Trump routinely spouts silly conspiracy theories where Biden normally seems to follow the science and the evidence. Trump has said and done numerous things that suggest he is a racist, whereas Biden on the whole hasn't. Trump routinely lies (as revealed for example by regular fact-checks of his interviews and Twitter feed) where Biden routinely seems to tell the truth. Trump has spent 4 years leading the most chaotic and clearly incompetent presidency in living memory, where Biden was previously vice-president in an administration that wasn't perfect but seemed pretty competent and professionally run. Trump routinely speaks words of hatred, seeks to provoke violence against opponents, and generally shows complete contempt for democratic traditions, where Biden appears to totally respect democratic principles.
But hey, dismiss them both as if they were equally bad, just because Biden doesn't come across as strong enough when he speaks?
