Out of all the Hillary vs Bernie debates, THIS is the most important fact that allowed Hillary to coast through the early primaries. The ugly reality is that the media bias in favor of Hillary was RAMPANT throughout 2015, even if both her and Bernie had announced their campaign early in 2015. This bias kept Bernie hidden from view mostly, while everybody fawned over Hillary's assured presidency. This is the grotesque hand that the media played all throughout 2015 and into 2016 to coronate Clinton, and to placate Bernie.
Just like in the UK, the media and his own Labor party attacked Corbyn, and yet he had a meteoric rise in popularity that got him great election results. In the US, Bernie's meteoric rise happened as soon as the first Democrat Primary debates in late 2015, (and he got notice after he was pulling crowds north of 28 thousand by August), because most Americans had not even heard what he was about (again, deliberate attempt by the media). Here is the Google search trends reflecting this fact, with people searching who Bernie was after the debate in January:
The early primaries in the South affected Bernie's chances, and by the time, the Clinton name was too embedded with the older folks that assured her the nomination. The media had done its part in twisting the Bernie campaign as a nuisance at the side of Queen Hillary.