The crucial factor in Trump's EC win over HRC was winning 2008 or 2008+2012 Obama voters. So it seems a little weird to say that a minority candidate cannot win, given that these were...Obama voters.
There are ofcourse hardcore racists who make up a huge part of the electorate. Short of reanimated Strom Thurmond, no Democrat will ever appeal to them. It is the former Obama voters and the huge numbers that stay home (disproportionately young, poor and minority), that need to be the Dem target votes. In the UK Corbyn seemed to have some success with non-voters, and Bernie-like numbers with young voters.
Except that Obama was a once in a lifetime candidate, not your average run of the mill "minority candidate".