FDR may have supported Bernie in the primary, but he would be with her now.
FDR was probably to the left of Sanders in actual policy terms but if we view both of those within the context of their times then Sanders is obviously well to the left of FDR. Bring FDR back and he'd almost certainly be a big Hillary supporter from the beginning of the primaries, even if he had quiet reservations.
Then you can look at losing nominees. George McGovern is often cited as the most left-wing major party nominee ever, but he wasn't that much different to many other Democratic senators of his day and was running against a Republican incumbent who was keen on price controls. Sanders stands out more today than McGovern did in his day. McGovern actually endorsed Wes Clark in 2004 IIRC.
