McGovern appealed primarily to affluent liberals and college students. He was clumsy about labor issues, and talked like a smug Ivy League professor. Sanders is different. He polls better than Obama did, or Clinton does, with working-class voters. The AFL-CIO hated McGovern; Clinton's backing from the AFT, etc. isn't remotely comparable to labor's support for Nixon. Also, McGovern ran against an incumbent.

Hillary's supposedly greater electability is just a media narrative repeated by her supporters. There is no solid evidence for it.