He's not a "deeply unpopular president." That's you exaggerating. But, it's still not a surprise that Biden isn't popular given that the theme has always been that neither presidential candidate is the one voters wants to see. Again, the poll is within a standard margin-of-error, is months away from the conventions themselves, and, isn't likely to reflect those who are undecided (which, at this point, is going to be a larger percentage than usual because of the candidates).