JoeChemist, when it comes to polls, the details matter, a lot.
“popularity” is not the same as “favorablility”. Sanders is viewed as “favorable” by about half the adult population. That population includes both people who go out and vote (like suburban whites), and people who are much less likely to vote (minorities).
Trump’s favorability rating is lower than Sanders’ on the general population (by about 10%), but is much higher (by almost 20%) among whites, who are more likely to vote.
Favorability in the absence of a race is not very informative, however.
Trump has an unassailable position in that his views encompass all the sacred cows of the United States: Borders must be protected, taxes are bad, immigrants bring in crime, intellectuals are dishonest, blacks belong in jail, browns steal jobs, gays corrupt our children, etc etc. Trump is in contact with the “soul” of America, and that makes him practically invincible.
Sanders favorability will be demolished within a day of campaigning. He will be portrayed as a communist Jew. Please don’t overrate the American People, they are far more ignorant, bigoted and stupid than you imagine. No offense here, just the truth.