From what I can see it's really just a race between Bernie Sanders and Donald Trump.
I don't see what's making everyone think Clinton will beat Bernie... Bernie is getting huge everywhere.
Most people think Clinton is going to smash Sanders because the signs are all pointing to it and have been since the beginning of the race.
Hillary is leading by quite a lot in all the credible national polls asking who people want to vote for. Bernie wins some online polls, which are naturally slanted toward a younger crowd and are less reliable because you can get mobs of people to go vote a particular way on it, unlike more serious polling done to try to get a representative sample of voters.
Bernie has a significant lead in recent polls that are specific to New Hampshire Democratic primary voters, and he has a decent lead in recent Iowa polls as well. Hillary is ahead in the other 48 states, and in most states it's a pretty killer lead.
The two above things are likely to shift even further in Hillary's favor now that Biden has officially said he's not running due to the fact that most of the people who were holding out for him are likely to go back to Hillary. Her shrinking lead in many polls coincided pretty closely with the rise in people saying Biden was their top choice, so it would be rather odd for them to all suddenly develop anti-establishment stances rather than going back to their initial candidate choice.
Finally, and perhaps most importantly, Hillary is ahead in the money game. The vast majority of the time in US elections in recent decades, the candidate with more money wins the race. She's not only ahead in actual campaign fundraising and cash on hand as of their most recent finance reports, she also has the extra advantage of making use of an affiliated super PAC that has also gathered millions of dollars in support of her. Sanders is against the very idea of these poorly regulated groups being allowed, so he hasn't formed an officially affiliated one and he has asked those who have created unaffiliated super PACs in support of him to knock it off. Odds are the Hillary's true fundraising lead will only grow further now that any pro-establishment wealthy Democrat donors who were holding out for Biden don't have that option any more.
Bernie is doing great for being up against the juggernaut of Hillary Clinton's campaign, but he is by no means in the lead just yet. It'll take a few weeks for polling to really get a good picture of the post-Biden landscape, but as of now he still has tons of work to do before people stop seeing Hillary as a sure thing.
I don't mean Obama voters as a whole. I mean the extra fluff he got that (probably) won him the election. The low-information voter that just voted based on a certain aspect, and not necessarily because they believe in or understand political motivations.
I think Trump has a lot of extra "fluff" support just like Obama had.
Ehh, very different kinds of "fluff" between them, so that's still a strange comparison.
Trump has people who want to vote for him because he's a recognized face/name, plus those who like him just because he doesn't give a shit about political correctness and says ridiculous things.
Obama had the progressive bump going for him, people who voted for him just because he's black. Those types are now mainly rooting for Clinton because they want to see a female president.