That's exactly what every president does when they're running for election. They present their ideas, the public votes for the most convincing option
What is your prefered candidate going to guarantee to do? Should I reconsider voting for them because I'm incredulous in my own biased perceived ability for them to deliver?
They can't guarantee anything. This is a machine with a lot of moving parts, all of which are required for it to run smoothly. A fundamental wrench in the machine during any Democratic administration, Sanders, Biden, Warren, Gabbard, etc. is a Republican held Senate which isn't going away anytime soon without a big fight. I think Sanders has the strategy to defeat Republicans in the Senate and extend Democratic control into 2022. The largest obstacle is corporate America, and now, the Koch brothers just announced they're willing to finance corporate Democrats campaigns who choose to play corporate ball, too, as a response to the progressive uprising within the Democratic party.