CNN — The confrontation in Atlanta between Joe Biden and Donald Trump Thursday night has a good chance of becoming the most fateful presidential debate in US history. For the first time, a sitting president and an ex-president will lock horns before millions of viewers, in an encounter taking place far earlier than normal — even before the party conventions. The CNN-hosted showdown is the most pivotal moment yet in a neck-and-neck election, and it’s Biden’s best chance to shake up a reelection bid that he is in deep danger of losing as he struggles to convince voters that he’s...