Biden is doing very well indeed in the polls and currently running ahead of Clinton at the same time in 2016. The reason? White voters. Two high-quality polls came out this weekend, Marist/NPR (A+ 538 pollster rating) and NBC/wall Street Journal (A- rating). Both had Biden ahead of Trump by 7 and both had Trump with minuscule leads (by recent GOP standards) among white voters: 5 points in the Marist poll and 6 points in the NBC poll. Nobody expects Trump to do well with the nonwhite electorate, but these figures among white voters are--if sustained--catastrophic for his re-election chances. He simply can't win with white support this low.
Loooooooong way to go but a very bad sign for Team Red.