Bernie is the most popular politician in the country.Go check his website. Pretty boiler plate standard Dem policies. He is against the wall, he is against the tax cut for the rich, he is for Medicare For All, he is for being in the Paris Climate Change agreement, he is for appointing liberal judges, etc, etc.
So anyone but Bernie, Warren or Tulsi. Which I agree with. Beto, Biden, Klobuchar, Kamala, Gillibrand, and so one would all beat him.
Of the "top tier' candidates the only one that would lose to Trump is Bernie and Warren.