Biden can survive losing Iowa and New Hampshire, but probably not if he places fourth or lower. That might trigger a stampede away from his candidacy as his "electable" narrative collapses.
Biden's like a shark - he either moves forward as the "perceived frontrunner" or he's dead in the water. He can weather a few narrow losses, but he's not the kind of candidate that can stage a remarkable underdog comeback after a string of early drubbings.
Also, his personal reaction to getting stomped in Iowa and New Hampshire would probably do a lot of damage to his campaign. He won't take it well, and he'll have a lot of cameras pointed at him with reporters pushing for comment. It's a recipe for utter disaster.
If the other candidates are serious about winning, they'll push hard after Biden takes a few losses and try to provoke him into coming unglued. Harping on how early primary voters clearly know Biden can't beat Trump, or how they're worried about corruption, would drive him nuts.
Biden's been trending down in South Carolina, his supposed firewall. He might get his firewall back if Bernie romps in the first few primaries and the Dem establishment panics - but then again, maybe some primary voters don't really trust their party establishment any more.
Iowa mostly tends to shake up the media, but it's kind of a sideshow for voters. The problem for Biden is he really needs the media treating him like the frontrunner, not buzzing about dismal performances and dramatic falls from the top of the polls. /end
