Hey guyzzzz...
First, we DO NOT have capitalism in the US as envisioned by Adam Smith or Keynes. We have a state-sponsored oligarchy, and it has been like this for over 40 years now. If you want to read the actual blueprint for corporations taking over our government since the 1970's (including funding/propping up Third Way Democrats like the Clintons and Obama), look up The Powell Memo. It was the birth of neoliberalism, and it was the beginning of the decline of the American middle and lower classes.
The answer is a candidate that will re-BALANCE the power AWAY from corporate cartels and lobbyists, and towards the American worker. The pendulum has swung MASSIVELY in favor of the wealthy since the 1970's (again, it was a rather coordinated coup by corporations), so all we see in the rejection of the failed status quo as we reach extreme levels of inequality, a severe lack of social mobility, and general anxiety (anxiety reflected in things like our opioid epidemic, and inter-racial tensions).
We also need a candidate, in these times of crisis for so many American families, (as in near 60% don't have $400 to survive the next emergency) that promises BOLD steps to accommodate and favor all those struggling Americans. Health care, education, student debt reform, etc. etc. etc. Who pays for it? how about the corporate welfare queens who have robbed our state of TRILLIONS UPON TRILLIONS of our dollars over the last 4 decades (facilitated by government at every step of the way). Imagine a candidate that promises a bottom up approach to American prosperity for the next 40 years!! Centrists utterly fail in thinking that all these American households have the patience (or the resources) to outlast "pragmatic slow progress" that amounted to SHIT under Clinton and Obama, and was being touted by Clinton as her basic message. She lost. We are at a point in American history when solutions need to happen NOW.
The FAST surge of Corbyn, the enthusiasm of young voters for Bernie and Corbyn, the snoozefest of a centrist Democrat promising the heavens without actually tackling the special interests that run our government... all the indications are clear on where the party needs to be. Corbyn made it despite his very own party, and the UK pro-corporate press. Unfortunately for us in the US, our pro-corporate press and the pro-oligarch Democrats were able to keep a tight lid on the progress Americans under 45 are clamoring for.