2020 vs 2016 - Real Clear Politics National Polling Averages as of September 7, 2016/2020Poll Average as of September 7, 2016 - Clinton vs TrumpClinton +2.1% (Clinton won the popular vote on election day by 2.9 Million votes and by the same percentage of +2.1%.)
Final Election Day Result: Clinton 48.2% / 232 Electoral Votes — Trump 46.1% / 306 Electoral Votes
* Note: After electors voted, faithless electors, who voted for someone other than their pledged candidate, caused Clinton's final electoral count to be reduced to 227 and Trump's to 304.
Poll Average as of September 7, 2020 - Biden vs TrumpBiden +7.1% (Biden's current polling lead is the same as the popular vote margin with which Obama handily beat McCain in 2008.)
Biden currently has a 5%
larger lead than Clinton had for the same time period in 2016, which is why you can expect Trump and his campaign to say or do practically anything between now and the election as the polling gap is clearly in the danger zone.
The graphs shown in the link below are fairly self-explanatory except for the top graph. The top graph shows a timeline with the blue portions showing the percentage increase that Biden has in polling compared to Clinton for the same point-in-time in 2016 and the red portion showing the percentage advantage of Trump over Biden compared to Clinton for the same point-in-time in 2016.
https://www.realclearpolitics.com/trump-vs-biden-national-polls-2020-vs-2016The Democratic candidate has won the popular vote but lost the electoral vote in two of the last five presidential elections. Due to the fact that electoral votes are
not proportionally distributed between voters and states, voters in low population states have a disproportionate weight in electoral outcome. As an example, California gets 55 electoral votes for 37.3 million people (2010 Census), or one electoral vote for approximately each 678,000 people. Wyoming receives 3 electoral votes for its 568,000 population, or about one per 189,000. In other words, the popular vote in Wyoming has
3.5 times the electoral weight of the same number of votes in California.
As the Republican candidate will sweep up a large number of electoral votes in lower population States — specifically those with relatively low population densities — with an electoral vote disproportionate to the size of their popular vote; the Democratic candidate will have to over perform and will likely require a popular vote win greater than the +0.5 that Al Gore received in 2000 or even the +2.1% that Clinton received in 2016 to insure enough electoral votes.
Obviously, with the unique Presidential election system in the US, the national popular vote doesn't determine the final outcome. However, a comparison of national popular vote margins to electoral vote victories, in past elections, will show that significant popular vote margins are generally reflective of a broader national sentiment and conducive to moving close swing-states and their electoral votes into the popular vote winner's column.
As examples of what a very healthy win looks like for a Democratic Presidential candidate, the Obama victories provide insight...
2008 - Obama 52.8% / 365 Electoral Votes — McCain 45.7% / 175 Electoral Votes. Obama popular vote margin +7.1% / +9.5 Million votes
2012 - Obama 51.1% / 332 Electoral Votes — Romney 47.2% / 206 Electoral Votes. Obama popular vote margin +3.9% / +5 Million votes