Even to skeptics, the presidential campaign of Senator Bernie Sanders of Vermont has often appeared less quixotic with the benefit of hindsight.

If Mr. Sanders had only edged Hillary Clinton in Iowa — and not the other way around — before winning a blowout in New Hampshire, perhaps things would have been different.

If he had only attacked Mrs. Clinton’s use of a private email server as secretary of state, instead of offering her a reprieve, some supporters lamented, perhaps things would have been different.

And now, as Mrs. Clinton contends with daily disclosures from the hacked messages of top campaign aides — missives that have reinforced the central progressive criticisms of her bid, including her coziness with Wall Street — some of Mr. Sanders’s admirers have been compelled to consider again what might have been.