I mean, at least for me, the question is “Who?”

In more ways than one. It’s quite evident to me now that a candidate needs to be charismatic, not just have some good ideas, to motivate voters to take their side. But “leftism” and “leftist” are still pretty vague labels. Just personally, some of the left-wing figures in the US today would earn my vote and some would not. More broadly, and I think there’d be a big difference between voters-at-large’s willingness to accept Bernie-esque proposals and some of the more out-there stuff I’ve seen.