I'm unfamiliar with how the Democratic primary works. Is it the same as how the GOP works? You really just need delegates right? If that's the case, can't the delegates choose to support Hillary instead of Sanders or are they forced to be Bernies delegates? I remember in 2012 when Paul kept claiming that the delegates could always support him instead of Romney
What you're missing is there are two types of delegates. Pledged Delegates are forced to vote based according to the caucus or primary results. For instance, Trump received 7 pledged delegates in Iowa - those delegates are forced to vote for him at the national convention unless Trump grants them permission to do otherwise. Same thing for the delegates that will be allocated to those who win a congressional district in say, Georgia, on either side - they are forced to vote for the winners of those CDs(or as otherwise specified under state party rules). Same thing for the 21 pledged delegates Sanders got in IA - they're forced to vote for him.
This is why Santorum and Gingrich formally released their delegates before the convention last time -otherwise, they would have been forced to cast meaningless votes for Santorum and Gingrich. These delegates were then not pledged to anybody and able to choose between Paul and Romney.
The second type is unpledged, or superdelegates. These aren't that numerous on the Republican side, but constitute 15% or so of democratic delegates. These delegates are unpledged for the entire cycle and can vote for anyone they like. This is where Hillary having a 300-delegate lead comes from - many of the superdelegates have endorsed her. They can change their mind at any time, however.
So, yeah, unpledged delegates could have voted for Paul, plus the delegates released by Santorum and Gingrich, in addition to those delegates required to vote for Paul. But it wouldn't have mattered if this happened, because there were around 1400 delegates who were required to vote for Romney. He only needed 1144 votes to be nominated. (The number thus year is 1237)
Also, note that most pledges only apply for the first ballot. This really only matters on the Republican side, where we still have more than 2 candidates. A formal vote is always taken at the convention, and if no one gets a majority, you just keep voting over and over again until you get a nominee. The way you avoid an eternal deadlock is through a part of the party rules that makes most delegates unpledged after the first round of voting.
