(CNN) Even as the White House this week firmly insists President Donald Trump is determined to seek a second term, a new analysis of polling data shows that he's caught in a three-way political squeeze in the states that tipped the 2016 presidential race, and will likely decide the 2020 contest.

On one front, Trump faces undiminished resistance from minority voters, who opposed him in preponderant numbers last year. On the second, he is confronting a consistent -- and, in many states, precipitous -- decline in support from white-collar white voters, who expressed much more skepticism about him last fall than GOP presidential candidates usually face. From the third direction, Trump's support among working-class whites, while still robust, is receding from its historically elevated peak back toward a level more typical for Republican presidential candidates -- especially in the pivotal Rust Belt states that sealed his victory.

These are among the key conclusions from a new analysis of the state-by-state Trump approval ratings released recently by the Gallup Organization. Those results, based on interviews with 81,155 adults in Gallup nightly tracking polls from January 20 through June 30, found that Trump's overall approval rating had fallen below 50 percent in 33 of the 50 states.

Extending beyond those reported results, Gallup provided me previously unpublished findings that tracked Trump's approval rating in key swing states among three demographic groups: non-whites, whites with at least a four-year college degree, and whites without a four-year degree.

Much, of course, will happen that could reshape the landscape between now and the next presidential election, which the White House this weekend insisted Trump plans to contest amid reports that Vice President Mike Pence and other possible contenders are preparing for the possibility the President might not run.

But these poll results challenge the conclusion that Trump's political base has remained impregnable across the traditionally decisive swing states in presidential politics -- as well as several other states that each side hopes to put into play by 2020. "The implications going forward are fairly problematic," says long-time Republican pollster Glen Bolger. "He doesn't have a lot of room to drop, and yet he is."

Trump approval down in key Rust Belt states

The 2018 Senate map is favorable to Republicans and could blunt the implications of Trump's erosion for the midterm election. As Gallup has reported, the President retains his strongest approval ratings in several preponderantly white interior states where Democratic senators will be seeking reelection next year -- including West Virginia, North Dakota and Montana; he's just below 50% approval in Missouri and Ohio, two other states with Democratic incumbents. But Trump is confronting approval ratings well below 50% in other states with marquee Senate races -- including Pennsylvania, Michigan, Wisconsin and Florida (where Democrats are attempting to hold seats) as well as Nevada and Arizona (where Republican incumbents could face their most serious challenges.)

"In 2016, there were two frames for the election: one was change, and the other was 'how do I feel about Hillary?'" says Bolger. "That was enough to win him the election. In 2018, the frame is going to be how do people feel about Donald Trump, how do they see him as president. Up to this point, that's not a real positive frame (for Republicans)."

Whatever Trump's effect on 2018, the Gallup results offer insights about the stability of the coalition he would likely need to assemble for 2020.

Gallup provided detailed demographic results for nine of the eleven states that both sides have recently treated as the most competitive battlegrounds -- including Virginia, North Carolina and Florida in the Southeast; Colorado and Nevada in the Southwest, and Ohio, Michigan, Wisconsin and Pennsylvania across the Rust Belt. Iowa and New Hampshire, the other traditional battleground states, did not have samples large enough to analyze with this specificity.

Gallup also provided detailed results from Arizona, Georgia and Texas, where Democrats are hoping demographic change will increasingly allow them to compete, as well as Minnesota, where Trump supporters hope that an older and predominantly white population will allow them to break a Democratic winning streak that extends back to 1984. Of the 13 states analyzed, Trump won all except Virginia, Colorado, Nevada and Minnesota.

A precipitous drop in approval from educated whites in key states

To assess the health of Trump's coalition across the 13 states, I compared his current approval rating with the share of the vote he won last November among each of the three key groups, according to exit polls posted on CNN.com. The comparison isn't exact because Gallup is measuring all adults, rather than actual voters, but the contrast provides one gauge of the health of his coalition across these pivotal states.

And despite the President's contention on Twitter Monday morning, that coalition is displaying some very pronounced cracks.

The most striking trend is the erosion of Trump's standing among college-educated white voters. Many of these voters have been ambivalent about Trump from the outset. In the general election he carried only 48% of them, down sharply from Mitt Romney's 56% in 2012. Yet, aided by widespread doubts about Clinton among these voters, Trump still bested her with them in nine of these 13 states while tying her in another (Pennsylvania).

But in the Gallup results, 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.)

The absence of Clinton as a factor

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.

Some of Trump's policies collide with the preferences of college-educated white voters (particularly on the environment, gay rights and immigration). But many of them (especially men) are also drawn to his lower-taxes, small government message. Like many observers, Greenberg believes Trump's biggest obstacle with these voters is not policy overall, but rather his blustery leadership style, which often stresses his disdain for expertise and stokes racial tensions. "It's cultural: everything [that's important] to the worldview of college graduates, he's disdainful of, " Greenberg says. "He's not just misaligned, he's at war with the idea of knowledge and information, science and progress, and tolerance and mutuality."

Compared to 2016, Trump's standing among non-white voters has changed less dramatically in most states. Last year he won about one-fifth or less of the minority vote in each of these 13 states except Florida (where he won about one-fourth), and Texas, Colorado, Arizona and Nevada (where exit polls put him around 30%.) In the states where Trump was weakest with minority voters, his current approval rating among them almost without exception runs only a point or two above or below his vote with them. In Florida and Nevada he's also seen minimal declines. But in Texas, Arizona and Colorado, relative to his vote, he's seen more substantial declines of seven-to-ten percentage points.

Dropoff in approval from less educated whites is less steep

The most important factor in Trump's victory last year was his superheated support among working-class whites. The Gallup numbers offer him a mixed picture on that front. His overall approval numbers remain much stronger among whites without a college degree than among whites holding advanced education: the Gallup findings place him at 60% or more among working-class whites in six of these states, and at 51% or more in the others except Minnesota (where he's just below at 48%).

But that 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.

Strikingly, though, Trump's job approval among working-class whites in each of those states has now receded to match, or even slightly trail, the level of support they provided Romney when he lost the same states to Obama. In Wisconsin, for instance, Trump's approval among whites without a college degree now stands at 51%, close to Romney's 53% vote share in 2012 but far below Trump's own 62%. Likewise, in Pennsylvania, Trump is now at 55% approval with non-college whites, almost exactly Romney's 56% vote in 2012, but well below the president's 64% among them. (Adding to the pressure, Trump's current approval among college whites in all four states is well below not only Romney's 2012 showing with them but also his own generally weaker 2016 numbers.)

More detailed results show Trump suffering relatively modest single-digit losses among working-class white men in these states. But, compared to his 2016 vote, his Gallup approval rating among working-class white women has plummeted in Wisconsin (down 18 points), Michigan (15 points) and Pennsylvania (13 points) and slipped in Ohio (down five points.) Greenberg points to the extended debate over repealing the Affordable Care Act -- and in particular cutting Medicaid -- as the key to that shift.

"The ones who are eroding are because he's going after their health care, because he's such a threat to social insurance that people depend on," he said. "In the campaign (he talked) about making health care affordable for all-it was a social democratic offer, it was not a (House Speaker Paul) Ryan offer. And for women, who are particularly focused on these health care issues, it's a real threat"

These working-class white women across the Rust Belt overwhelmingly rejected the first female major party nominee last fall, giving Trump big majorities of their votes in all four states. That backing was pivotal, and arguably decisive, in electing him president. Seven months into Trump's presidency, with resistance to him widening among white-collar whites and hardening among minorities, rebuilding his support among those women looks more critical for him than ever.