It's either the luckiest or most genius move in political history, but replacing Joe Biden is a masterstroke on every level. It kills the relentless momentum Trump built up from the debate debacle and being shot, it focuses the biggest weapon the Republicans has against the Democrats, Biden's age, right back on their own candidate, and it re-energizes the Democrat vote. Trust me, Trump wishes he'd lost that debate. The question now is, having used up all their nine lives, will the Democrats make the right choice?