(CNN) President Donald Trump heads into the debate trailing former Vice President Joe Biden. Trump is the first incumbent to be losing in the polls at this point since George H.W. Bush in 1992.
Trump's obvious goal for the debate is to try and win back some of the White voters without a college degree that he's clearly lost since 2016. In doing so, he might be able to stop Biden's easiest paths to taking back the White House for the Democrats.
Take a look at the live interview national polls taken since the conventions that meet CNN standards for reporting. We're talking about nine polls in total from eight pollsters, so it's a large sample.
View 2020 presidential polling
Trump is winning by about 21 points among Whites without a college degree in an average of those polls. That may seem like a lot, but remember that Trump led among this group by about 30 points in the final pre-election polls in 2016.
Keep in mind, we're making an apples-to-apples comparison here. Even if the polls are off by a similar margin as they were in 2016, this exercise takes that into account. There's real movement going on here among Whites without a college degree.
This 9-point or so shift is even more impressive, when you keep in mind that there's been a change of less than 4 points overall toward Biden compared to where Hillary Clinton was at the end of 2016.
In other words, there has been a disproportionate shift toward Biden among White voters without a college degree.
These voters make up the majority of voters in key Rust Belt (Great Lake) battleground states such as Michigan, Pennsylvania and Wisconsin. All of these were states Trump won by less than a point in 2016.
How the candidates are preparing for the first debate
Not surprisingly, Biden's position in these states has significantly improved from where Clinton ended up. He's got a 5- to 7-point advantages in all of these states.
We see similar big shifts toward Biden compared to Clinton in other key states in the region: Iowa and Ohio. Biden's about even in Iowa and slightly ahead in Ohio, despite Clinton losing them by 9 and 8 points respectively. Again, both states have a lot of White voters without a college degree.
The shift toward Biden in these states is larger than the shift in some other close states that Trump barely won in 2016. Biden isn't doing nearly as well as Florida or North Carolina, where White voters without a college degree are less than a majority of the electorate.
Indeed, Arizona is the only state of the six closest won by Trump in 2016 that doesn't fit this pattern. Whites without a college degree don't make up a majority of voters in Arizona. Yet Biden has about a 3- or 4- point lead there, even as Clinton lost the state by 4 points.
That discrepancy can easily be explained by the fact that Democrats have also seen big gains among Whites with a college degree nationally (specifically suburban) as well, and Arizona's White voters with a college degree are merely catching up from a low baseline to the nationwide average among this group.
When you put it all together, Biden's easiest paths to the presidency revolve around two potential maps.
The first is he has to win the states Clinton won in 2016, as well as Michigan, Wisconsin and Pennsylvania. This gets Biden to 278 electoral votes. Based purely on the polling, this looks like Biden's best bet at the moment.
The second is Biden has to win the Clinton states, Michigan, Wisconsin, Arizona and Nebraska's 2nd congressional district (the winner in each congressional district in Nebraska gets an electoral vote). This gets Biden to exactly 270 electoral votes.
Both maps rely heavily on Biden doing better than Clinton among Whites without a college degree in the Great Lake battlegrounds.
The question heading into the debates is whether Trump can do anything to knock those voters away from Biden. If he cannot, Biden's likely to be the next president.