Basically, the national polls simply don't matter. Trump faces such a huge electoral college disadvantage that he will have to win every battleground state AND steal a safe blue state such as Pennsylvania or Michigan. That simply isn't going to happen.
According to the Princeton professor, the bigger suspense is with the Senate. The Democrats only have a 76% chance of winning back the Senate.
The House of Representatives was not discussed. I'm sure that's a bigger long shot for Democrats, due to egregious Repug gerrymandering in several states such as N. Carolina and Pennsylvania. Gerrymandering won't save Repug control of the House much longer, maybe a couple more election cycles. Gerrymandering is the Repugs' only way of maintaining control of the House this year.