I don't know whether Biden should step down at this point or not, but I'm not convinced that because 1968 went poorly for Democrats the same would be true this time. Biden's age is not an ideological issue splitting the party in the same way that Vietnam was
Gaza has some similarities to Vietnam, but that can be overstated--there's no draft!--so creating a bit of distance from the current administration could help bring the coalition together
I would just really seriously prefer that we not be going into a very probable war with Iran with a Commander in Chief who, based on his staff's admission, is coherent for less than a standard shift at work