Ever since Inauguration Day, the public’s faith in the president has been eroding. According to the latest Gallup surveys, only about 38 percent of Americans approve of Trump’s performance, which is down roughly 5 points from February. Vox’s own polling, conducted in partnership with SurveyMonkey, shows a similar drop — from 46 percent at the outset of his term to 41 percent in July.

For the president’s critics, these slipping approval numbers seem like vindication. They show that Americans aren’t blind to the disorder in the White House — that at least some Trump supporters are second-guessing their president.

But what does this mean in practical terms? American politics, by design, has never perfectly followed public opinion. After all, Trump never had a majority of Americans rooting for him. He won the Electoral College but lost the popular vote. What’s important isn’t his popularity nationwide but his approval rate in key parts of the country.

Democrats, for one, hope that the growing disenchantment with the president will translate into congressional victories come 2018. But according to an analysis of more than 50,000 respondents of Vox/SurveyMonkey polling, the prospects of a midterm Democratic surge still look shaky.

Most of the decline in Trump approval, it turns out, occurred in congressional districts that are already solidly red or solidly blue. In the closest Republican districts, opinions of the president haven’t budged at all over the past six months. Overall, Americans may be growing weary of Trump’s chaotic administration — but it seems the Americans who will matter the most politically next year have yet to change their minds.

Close Republican districts are an anomaly

Over the past six months, Vox and SurveyMonkey have been polling Americans about their opinions on the president and the economy. By grouping people according to where they live, we can get a sense of Trump approval in different regions. The nation has 435 voting congressional districts, but the most important ones are those that occupy the middle of the political spectrum. These are the swing districts that determine the relative clout of the parties in the House.

In solid Democratic districts — places where the Democratic House candidate won overwhelmingly in 2016 — Trump approval slipped from an average of 32 percent in February through April to 29 percent in May through July. Likewise, in solid Republican districts, Trump approval fell from 56 percent to 53 percent. Though these are statistically significant declines, they don’t mean much politically, because these districts will practically never be in play.

In the 50 closest congressional districts on the Republican side, though, Trump’s approval rating has held steady at 47 percent. Meanwhile, among the 50 closest districts on the Democratic side, Trump approval seems to have declined from 42 percent to 39 percent (though it’s still too close to call).

This pattern becomes clearer when we focus on people who say they “strongly” approve of the president. In close Democratic districts, that percentage fell noticeably over the past six months, from 23 percent to 20 percent. But in close Republican districts, enthusiasm for the president hasn’t changed: 26 percent of people continue to strongly believe that Trump is doing a good job.

In other words, the polling suggests that Democrats might be tightening their grip on close districts they won in 2016, but they haven’t made any progress on the districts they hope to flip in 2018 — at least not if Trump’s approval is any indicator.

Most Republicans turning against Trump live in Democratic districts

Close congressional districts are close because they contain an even mix of people from both sides of the aisle. Opinions about the president are extremely polarized by political affiliation — among Republicans and right-leaning independents, the Trump approval rate remains well over 80 percent. Among Democrats and left-leaning independents, the approval rate is less than 10 percent.

Even Republicans are starting to change their minds, however. In February, 90 percent of right-leaning Americans approved of Trump. By July, that number had fallen to 86 percent.

But it seems that most of those Republicans turning against the president hail from Democratic congressional districts: In safe Democratic districts, the Republican approval rate has fallen from 86 percent to 82 percent. And in close Democratic districts, it’s fallen from 89 percent to 84 percent. These are statistically significant changes.

Here’s the bad news for Democrats: Republicans in close Republican districts remain upbeat about Trump. There, approval rates appear to have dipped from 91 to 89 percent, but it’s a difference that is too small to be statistically significant.

Again, the phenomenon is easier to see when we look at those whose are especially enthusiastic about the president. In close Democratic districts, the percentage of Republicans who say they “strongly” approve of the president fell dramatically, from 59 percent in the first three months of his term to 51 percent in the most recent three months.

But among Republicans living in close Republican districts, the rate of enthusiastic Trump supporters has held at around 56 percent. That contrasts with what’s happening in solid Republican districts, where the rate of Republicans who strongly approve of the president has fallen from 61 percent to 56 percent.

It appears that in congressional districts held by Republicans, there remains a core group of right-leaning voters who don’t seem concerned about the messy dramas emanating from the White House.

The pattern is the same when we narrow the focus to the closest 25 congressional districts on either side. (The pattern also persists when we look at close counties, which rules out gerrymandering as an explanation, since county lines are not regularly redrawn for electoral reasons.)

So what’s happening here?

It’s important to point out that the data set we’re using is massive, but not without its caveats. Our 50,000 respondents come from online surveys, and while this a nationally representative sample, it might not precisely capture the opinions of those who shun the web. Furthermore, our results end in the first week of July (our August survey is currently in the field), so they don’t reflect the latest shifts in public opinion. A lot happened in July — the Don Trump Jr. emails, the failed Senate health care bill, the brief, wondrous White House career of Anthony Scaramucci — and other polling suggests that these controversies have caused Trump approval to slip further in recent weeks.

What’s safe to say is that Trump approval has remained surprisingly resilient in the places that matter most to Democrats right now: the districts they hope to win in 2018.

Our polling data also casts a different light on the special House elections of the past few months, where Democrats have made startling gains. In the high-profile race for Georgia’s Sixth, for instance, Democratic challenger Jon Ossoff nearly defeated Republican Karen Handel, even though the district went Republican by a 62-38 margin in 2016. (For reference, GA-6 doesn’t even count as one of the 50 closest Republican districts.)

Many pundits took the close Ossoff-Handel race as a sign that backlash against Trump would trigger a Democratic surge in 2018. Overall, though, our surveys suggest that Democrats will have a tough time in vulnerable Republican districts, where opinions about Trump have been slow to change — particularly among the Republicans and swing voters that Democrats will need to rely on to win seats.

All of this seems to be another sign that Americans are divided, not only by ideology but by the information they consume and the company they keep. Trump approval might be declining across the nation, but not so much in the Republican enclaves that Democrats desperately hope to flip.