Did Democrats “Clear the Field” for Hillary Clinton in 2016?

Dennis Van Tine/UPPA via ZUMA

There are pros and cons to be being a blogger. One of the cons is that when you ask a question that shows off your ignorance, the entire world gets to see it. Let’s do it anyway.
Question: What exactly do people mean when they say that the Democratic establishment “cleared the field” for Hillary Clinton in 2016? I can think of various definitions of this, ranked from least to most objectionable:

HRC had lots of money and lots of support, and that scared everyone else away.
Democratic bigwigs actively lobbied prospective candidates to stand down.
HRC made various promises to superdelegates, but only if they’d support her and make sure that everyone knew they wouldn’t switch.
The establishment threatened prospective candidates in concrete ways if they showed interest in running.

#1 is meaningless. Someone is always the frontrunner. #2 is more active, but also a nothingburger. #3 is worse, depending on what kind of promises were made. #4 would be clearly beyond the pale.
So what is it? I’m not plugged into the gossip circuit, but I was paying attention during 2015 when candidates were thinking about running. I don’t recall hearing about anything untoward during that time. In fact, what I mostly heard were laments about how thin the Democratic bench was. Anyone care to help out here? I especially want to hear from Bernie supporters who feel like the Democratic establishment screwed them.