I have concerns about the candidacy of Bernie Sanders. They do not have anything to do with his competency; I think his campaign, to date. has proven his bona fides in that regard. To a lesser degree he has proven his ability to get his message across to a large group of the electorate.
No, my concerns aren't about Bernie but they are about the Democrats that could elect him to the Presidency. We could see a repeat of what happened to the Obama Presidency, with crowds of people voting for him in the Presidential election but who sat on heir hands, in the off years, allowing the Republicans to not only win majorities in both Houses and obstruct Obama that much more but also win statehouses so they could restrict that part of the electorate that constituted the Democratic support.
As Bernie says, he wants and needs a political revolution to accomplish what he wants to do, and I just doubt that he can ever get one with the Democratic electorate as presently constituted. After all, if ever there was an opportunity, it was at the time immediately after the economy tanked in 2009. When the going got tough, with Republican obstruction, the Democrats jumped ship in 2010. A political revolution, in good economic times, like now, is probably a bridge too far for Democrats.