Convention won't go to 2nd ballot. Anyone telling you it will is engaging in fear-mongering as badly as the red baiting over Bernie's Castro comments or is a stupid pundit, IMO!
OMG the Super delegates are coming! OMG they'll steal this election from us which ignores the DNC First Ballot rules AND Democratic Party history.
OMG Sanders is a Castro loving Commie coming to take away your freedoms! OMG he'll flip Florida to the GOP which is ridiculous charge since we already lost it in 2018 due to FL Democratic Party's continued failure to counter the FLGOP's massive Latino outreach program.
This type of non-stop fear-mongering is as corrosive and intellectually dishonest as Trump's OMG the migrant caravans are coming to invade white AmeriKKKa.
Delegates elected to the national convention pledged to a presidential candidate shall in all good conscience reflect the sentiments of those who elected them.
Beyond this, the Delegate Selection Rules do not directly address how a candidate's withdrawal from the race before the convention affects the delegates pledged to that candidate. However, in 13 states, statutes establish provisions for the release of delegates either upon a candidate's withdrawal or after a specific number of ballots have been taken at the national convention.
https://ballotpedia.org/Democratic_delegate_rules,_2020
In the other states and territories, pledged delegates are freely allowed to change their vote for a different candidate on the first ballot if they are "released" by the candidate they are pledged to. While not bound by their candidate's endorsement to vote for a different candidate, that's usually the practical result.
In the 2008 primary, Barack Obama failed to secure a clear majority of pledged delegates. I repeat Obama only won a plurality of the pledged delegates. This fact appears to escape those screaming OMG super delegates may decide who is our nominee. Newsflash they already did in 2008!
On June 3, 2008 Obama announced he had secured enough pledged AND super delegates to surpass the majority required for the nomination.
The Clinton campaign pushed back hard for a few days, arguing, as ironically Bernie Sanders later did in 2016, that super delegates could change their minds at the convention and thus, she still had a viable path to win. Clinton's claim was met with such fierce pushback, she backed down and officially conceded a few days later.
Clinton formally released her delegates during the 2008 first ballot vote roll call and moved by acclamation the convention nominate Obama.
Breaking with tradition, in 2016 Sanders chose to wait until the formal roll call vote concluded before releasing his pledged delegates and moving to nominate Hillary Clinton.
When pledged delegates are released could play a decisive role in the 2020 nomination process.
For one example, Pete Buttigieg could amass 8% of the pledged delegates then play "kingmaker" by formally releasing his delegates and asking them to vote for Joe Biden, instead. Conversely, Warren could play "kingmaker" by releasing her amassed pledged delegates and asking them to vote for Bernie Sanders.
It is also possible two or more candidates with small pledged delegate counts could bind together and play "kingmakers and queenmakers."
In the old smoke-filled convention days, these negotiations sometimes led to the formation of a Unity Ticket. Say what you will about JFK and LBJ's contentious relationship, but they were united in their desire to defeat Nixon in 1960.
And, that is the type of unity we must have in 2020 to defeat Trump, and most Democrats do understand he is the real enemy.
In 2008, Obama was urged to pick Clinton as his VP to unite the party. Instead, he chose a different rival, Joe Biden, and later explained he considered Clinton a better fit for his Secretary of State.
Some diehard PUMAs notwithstanding, Obama and Clinton succeeded in uniting the party in 2008. In 2016, Clinton was urged to pick Sanders and chose Kaine instead, a move some saw as failing to unite the party.
If any candidate fails to secure a majority of pledged delegates, they face their first big challenge, can he/she build a coalition to achieve their first big goal of beating Trump in November?
If Sanders can't win over enough support within Democratic Party, how in hell does he expect to beat Trump and stand a chance to build support for his dream of M4A? If Biden can't win enough support within his own party of 50+ years, he has no business going up against Trump either.