According to an analysis from Ron Brownstein, Trump’s standing in precisely those states that delivered the presidency to him is sinking. Photo: Mark Wallheiser/Getty Images

There has been a robust debate in the political commentariat throughout the year about the president’s approval ratings and what they portend for 2018 and 2020. It’s generally conceded (though not by the president himself, who argues the size of his rallies is the best indicator of his popularity) that Trump’s already weak public standing has softened somewhat. But there is less agreement about where he stands with this or that part of the electorate — particularly his “base,” however that is defined.

But now Ron Brownstein, working with some previously unpublished Gallup data from 13 current and projected battleground states (Arizona, Colorado, Florida, Georgia, Michigan, Minnesota, Nevada, North Carolina, Ohio, Pennsylvania, Texas, Virginia, and Wisconsin), has given us the best snapshot yet of exactly where, geographically and demographically, Trump stands as compared to his performance last year. It shows that he is hemorrhaging the most support from college-educated white voters, though he’s lost a crucial bit of his strength from the non-college-educated white voters often considered his “base.”

Trump’s approval rating among college-educated whites has declined relative to his 2016 vote in all 13 states. In seven of those states, his approval rating stands at least 10 points lower than his vote –a list topped by North Carolina and Florida (both 19 points lower), Georgia (18 points lower), Ohio (15 points), Virginia (12 points), and Michigan and Minnesota (11 points each.) His approval rating among these white-collar whites reaches above 50% only in Texas and Georgia, and exceeds 45% in just two other states, Nevada and Arizona. In seven states, his approval among these well-educated white voters has tumbled to 40 percent or less. (That includes four states essential to his victory: North Carolina, Michigan, Pennsylvania and Wisconsin.)

Some might object that Trump managed to win last year despite poor approval numbers then. But that cuts both ways: In 2016, Trump was competing with a pol who was nearly as unpopular as he was. Hillary Clinton will not be on the ballot or in the consciousness of voters in 2018 —or presumably in 2020, either.

These anemic numbers suggest how much Trump benefited last fall from the doubts these voters also held about Clinton; standing alone, without her as a foil, he’s facing much harsher assessments. (In a separate national Quinnipiac University poll released last week, 59% of college-educated whites said they “strongly” disapproved of Trump’s performance.) “I think the doubts about her blocked how big the potential was for those voters to vote against Trump,” says long-time Democratic pollster Stanley B. Greenberg.

Relatively speaking, Trump’s support is holding up better among white working-class voters, the core of his base. But there are still problems:

[Trump’s] standing still represents an erosion from his 2016 vote among blue-collar whites in 12 of those states; in five of them, he’s declined by double-digits. Perhaps most important are the trends in four of the Rust Belt states that proved decisive last year: Michigan, Ohio, Wisconsin and Pennsylvania. In all of them exit polls found Trump won between 62 and 64% of non-college whites. In each case, that was a substantial increase from Romney’s performance with those voters in 2012, when former President Barack Obama carried the states.

In those four crucial states, which were where the 2016 upset was consummated, Trump’s white-working-class approval numbers are down around the levels of support Romney achieved in losing all four in 2012.

We sometimes forget in our awe at Trump’s astonishing rise to the presidency that it was a near thing, particularly in the general election. He doesn’t have much margin for error, and nor does his party in a midterm election that usually represents a referendum on the party controlling the White House (and in this case, the much-despised do-nothing Congress as well). The drops in support among white voters in battleground states that Brownstein documents aren’t massive, but they could spell the difference between Republican success and calamity just down the road.