Bill didn't "campaign to the left". He was the leader of something called the "Democratic Leadership Conference", a group of mostly southern Democratic moderates, urging the Democratic party to reconnect with their working class roots and abandon unpopular extremist positions. When Clinton won the nomination, it was widely speculated that he would select a more liberal candidate for Vice President, but instead he went with fellow DLC member Al Gore.
It is widely believed that he secured victory with the famous "Sister Soulja" moment, where he condemned a rap singer for song lyrics that advocated violence. That separated him from some Democratic candidates who would instinctively defend the popular black artist, making excuses for the violent rhetoric.
I'm not sure I would say that Barack Obama campaigned to the left, either. He condemned the fiery rhetoric of the Reverend Wright. To be honest, I don't remember what separated him from other rivals for the nomination when it came to policy or attitude. I don't even remember who those rivals were, other than Hillary Clinton. I don't think he campaigned "to the left" of Clinton. I just think he was more charismatic.
The serious lefty in 2008 was Dennis Kusinich - who was regarded as a joke. Edwards ran, lost, and was destroyed by an affair. Biden ran, fairly centrist, and...well, you know. I think Gravel ran - only remember his name because he's trying to spin up a progressive answer to PragerU on Youtube (a very good idea).
And then there were some other people, nobody cared about them.
I said the entire time that when you looked at actual positions, Obama and Clinton were pretty close - same basic health care system, same basic view on wars, rights, and so forth. No real distance on immigration, which wasn't a massive issue among dems in any case. It was mostly identity, and "did you vote for the Iraq war?", which Obama won by default.
Yes, Obama promised "change", and a lot of people read what they wanted into that, decided that he abandoned on withdrawing from Afghanistan (he wanted a "surge" there) and Medicare for all (which he outright rejected during the campaign, and couldn't possibly pass in the senate long-term anyway - Lieberman alone pretty much blocked Medicare expansion just to piss off the left).
ETA: the thing that struck me about Obama's condemnation of wright was how much he concentrated on Wright saying "Obama is a politician, and speaks in the way politicians do. I'm a reverend, I speak the way reverends so." Both of these are...perfectly correct, really. And I was always amused by the hysterics over Wright's "God Damn America", leaving out "For killing innocent people, that's in the bible!" from the same people who nod approvingly when some televangelist says God sent some hurricane to America to punish us for letting dudes kiss in public.