(CNN) Though the 2018 election opened intriguing opportunities in the Sun Belt, new data suggest the shortest path back to the White House for Democrats may be through the three Rust Belt swing states that President Donald Trump dislodged from the "blue wall" two years ago.

The party will have to choose -- with its nominee, its resources and its message -- whether it wants to focus most on rebuilding that wall -- or on expanding its opportunities in a new set of emerging battleground states across the Sun Belt.

As both parties pick through the results of this month's midterm for clues about possible shifts in the 2020 presidential map, previously unpublished results from the Election Day exit poll show that Trump faced pointed erosion in approval of his job performance from a wide range of critical groups in Michigan, Wisconsin and Pennsylvania, the three states that keyed his victory in 2016. In particular, the exit polls showed that in those three states Trump not only faced surging opposition from college-educated white women, but also suffered notable attrition among the blue-collar white women who were critical to his success there last time.

Those exit poll results reinforce the evidence from the elections themselves, in which Democrats held a Senate seat and won the governorship in each state, while also gaining a net of five House seats in Pennsylvania and Michigan combined. All of those results have cemented a quick consensus among many Democratic strategists that those three states, which Trump carried by a combined 80,000 votes in 2016, represent the weakest link in his Electoral College majority.

"The quickest way to win again is to get those three states back into the Democratic fold, and I think we've already seen tremendous evidence they are ready to come," says Tad Devine, who helped to manage Electoral College strategy for Democratic presidential nominees from Michael Dukakis to Al Gore and served as a top adviser to Bernie Sanders in 2016.

Since World War II, the results of midterm elections have not consistently predicted the outcome of presidential contests two years later. Poor showings by the president's party in the midterm elections of 1958, 1966, 1974, 1978 and 2006 did foreshadow a switch in control of the White House in the next presidential election. But first-term presidents rebounded to win re-election after significant midterm losses in 1946 (Harry Truman), 1954 (Dwight Eisenhower), 1982 (Ronald Reagan), 1994 (Bill Clinton) and 2010 (Barack Obama).

But strategists in both parties believe midterm results can signal shifts in the political currents within individual states. And those changes can influence each side's calculations about the most promising path to amassing the 270 Electoral College votes required to win the White House.

The widespread Democratic gains earlier this month, especially in the House, buoyed the party's hopes of ousting Trump in two years. But they also ignited an immediate debate about whether the most promising option was to recapture the Rust Belt states that Trump flipped in 2016 or target Sun Belt states where Democrats notched clear gains in 2018, even while falling short in the governors' races in Georgia and Florida and the US Senate race in Texas.

Fresh insights on that question emerge in new data from the exit poll provided by Edison Research, which conducts surveys for the National Election Pool, a consortium of news organizations that includes CNN.

The Election Day exit poll asked voters whether they approved or disapproved of Trump's job performance. At CNN's request, Edison analyzed Trump's job approval in the key swing states along lines of race, gender and education.

Those results pointed toward clear opportunities for Democrats in the potential 2020 Sun Belt battlegrounds. But they also left little doubt that Trump is most exposed in Michigan, Wisconsin and Pennsylvania. Those were the three states he dislodged from what I termed the "blue wall," the 18 states that had voted Democratic in all six presidential elections from 1992 through 2012.

A close balance in the Sun Belt

In the key Sun Belt states where exit polls were conducted this month, Trump's approval rating consistently hovered right around the critical 50% mark. That ranged from a high of 52% in Georgia and Arizona to 51% in Florida, 49% in Texas and 48% in Nevada.

In all these states, Trump demonstrated overwhelming strength among his core constituency of white men without college degrees: His approval among them, according to the exit polls, ranged from 67% in Arizona to 69% in Florida and Nevada to 76% in Texas and fully 80% in Georgia. His numbers among white women without college degrees across the Sun Belt were only slightly less imposing: Those ranged from just under 3 in 5 approval in Nevada, Arizona and Texas to two-thirds in Florida and over 4 in 5 in Georgia.

Among college-educated white men, Trump maintained imposing margins in Florida, Georgia and Texas, but they divided about in half over his performance in the Southwest battlegrounds (Arizona and Nevada).

Among college-educated white women, the pattern was similar, with one twist. Trump was competitive in Texas and Georgia (where these women split about evenly over his performance). But he faced more widespread resistance again in Arizona and Nevada, this time joined by Florida; about 3 in 5 of them disapproved in each state.

Among minorities, Trump faced disapproval ratings exceeding 60% among nonwhite voters both with and without college degrees in Arizona, Nevada and Texas, states where Hispanics dominate the minority population; in Georgia, where most minorities are African-American, Trump faced a minority disapproval rating of almost 80%. In Florida, where both groups are present, he faced disapproval from just over 3 in 5 nonwhites with degrees and fully 7 in 10 of those without, though the Republican US Senate and governor candidates showed surprising resilience with Hispanics in the state.

The narrow overall verdict on Trump's first two years suggests that all of these Sun Belt states could be competitive in 2020. But the results do raise red flags for each side. Nevada was one of the Hillary Clinton-won states Trump's camp hoped to target in 2020, but both the election results (Democrats elected a governor and senator) and the exit poll findings (with his weakness among college-educated white men and women and limited support among Hispanics) suggest that will be a very tough climb for him. And while there was no exit poll in Colorado, the Democrats' strong showing there, particularly in the white-collar Denver suburbs, sends the same message (as well as pinpointing staunchly pro-Trump Republican Sen. Cory Gardner as perhaps the GOP's most endangered incumbent in 2020).

Democrats will face a choice of resources

On the other hand, Trump's overwhelming support among non-college white men and women in Texas, Georgia and Florida underscores the challenge for Democrats of winning those states in a presidential year, when working-class whites usually turn out in higher numbers.

Democratic strategists are insistent that Florida remains a "coin flip" between the parties (particularly after a US Senate race decided for Republican Rick Scott by about 10,000 votes out of more than 8 million cast). But based on these patterns, the party will likely face a more intense debate than previously about how much time and money to invest in the Sunshine State.

Rep. Beto O'Rourke's sweep of Texas' metropolitan areas in his unexpectedly strong showing against Republican Sen. Ted Cruz showed Democrats a viable pathway to competing in the state. And if O'Rourke is on the ballot again in 2020 -- whether in either slot on the Democratic presidential ticket or in another Senate race, against Republican Sen. John Cornyn -- the state may look more attractive to Democrats at the presidential level.

"If he's back on the ticket, any presidential candidate is going to invest in Texas," predicts Austin-based Democratic consultant James Aldrete.

But if O'Rourke himself isn't the nominee or vice president, it remains unclear whether any other presidential candidate could commit to the enormous television advertising that would be required to seriously contest the state. "If you are going to come into that with real resources, that could be worth a half-dozen other states," notes Devine.

Beyond Florida, the Sun Belt states that emerged from the 2018 results as the most widely agreed-on targets for Democrats are likely Arizona and North Carolina. Though an exit poll was not conducted in North Carolina, the election results there showed continuing Democratic strength in suburban areas. But the results also suggest Democrats may face the same 2020 headwind as in Georgia, Texas and Florida: little erosion for Trump in the blue-collar and rural communities that powered his victory last time. Arizona may be the most promising new Sun Belt opportunity of all, with Democratic Rep. Kyrsten Sinema's US Senate win over Rep. Martha McSally providing clear evidence that white-collar suburbanites there moved away from the GOP even more than their counterparts in Texas or Georgia. Maricopa County, surrounding Phoenix, was the largest US county that Trump carried in 2016, but Sinema won it by about 60,000 votes.

A new shine on the Rust Belt

Sen. Sherrod Brown celebrates his campaign victory at the Hyatt Regency on November 6, 2018 in Columbus, Ohio.

Across the Rust Belt, with one glaring exception, the evidence from 2018 looks more consistently encouraging for Democrats. Generally, Trump's overall approval rating in the exit polls across the key Rust Belt states was slightly lower than in the Sun Belt states.

In Minnesota, the Midwestern state Republicans most hoped to flip to Trump in 2020, the results and the exit polls offer him little encouragement. Democrats won two Senate seats (including a special election) and the governorship, and the exit poll put Trump's approval at just 45%.

Conversely, the most daunting Rust Belt results for Democrats came in Ohio. Though Democratic Sen. Sherrod Brown, a potential 2020 contender, won re-election, his margin was narrower than expected and Republicans comfortably held the governor's mansion. In the exit poll, 52% of Ohio voters approved of Trump's performance. And while college-educated white women tilted slightly away from him (with 52% of them disapproving), he retained very strong numbers there among non-college white men (67% approval), college-educated white men (62%) and non-college white women (59%).

But, if anything, Trump's continued Ohio strength among those groups only underscored his more precarious position with them in the other key Rust Belt battlegrounds of Wisconsin, Michigan and Pennsylvania.

"I think Ohio is much more of a core red state than the other three," says John Brabender, a Pennsylvania-based GOP strategist. "The other ones are at their hearts blue states that will sometimes vote Republican. And it better be an awfully good year."

In the exit poll, Trump's approval rating among voters stood at only 44% in Michigan, 45% in Pennsylvania and 47% in Wisconsin. In each state the share of voters who strongly disapproved of his performance exceeded the share that strongly approved by at least 15 percentage points, a daunting margin.

Across the three states, key demographic groups also reacted to Trump in similar ways. Among white men without college degrees, Trump remained strong, drawing positive job marks from 70% of them in Pennsylvania, 65% in Michigan and a somewhat more equivocal 57% in Wisconsin. He remained relatively solid, though somewhat diminished, among college-educated white men as well, winning approval from nearly 3 in 5 in Wisconsin, just over half in Michigan and just under half in Pennsylvania.

Republicans lost support from Rust Belt women

But Trump showed conspicuous weakness with women across all three states. His disapproval ratings among college-educated white women reached 69% in Pennsylvania, 67% in Michigan and 64% in Wisconsin.

Perhaps even more ominously, his disapproval rating in the three states among white women without college degrees spiked to between 46% and 48%, considerably more than in any other battleground state. His approval rating with them in each state stood at just 51% to 53%. That was closer to his unsteady position with those women in Democratic-leaning Minnesota (where they divided about equally over his performance), than in more reliably Republican Ohio, Indiana and West Virginia.

In most places, Democrats were frustrated by their inability to recover more ground with working-class white women (56% of them voted Republican in House races, according to the exit poll). But in the three states where those women will likely matter most in 2020, they displayed clear second thoughts about Trump.

Brabender says these reactions capture "the paradox" of Trump's style: While his iconoclastic and often belligerent language convinces many working-class voters, especially men, that he's committed to shaking up the system on their behalf, it also alienates more moderate voters, especially women. "The paradox is that what the others see as evidence this is going to be a different type of president, among some of the more moderate voters, particularly women, they have problems with that tone," he says.

Because African-Americans compose the preponderance of the minority population in Michigan, Pennsylvania and Wisconsin, Trump's approval rating among nonwhite voters is also lower there than in most of the Sun Belt states.

All these patterns loom over the upcoming Democratic presidential primary.

Two types of Democrats to challenge Trump

Sens. Kamala Harris and Cory Booker attend the Senate Judiciary Committee confirmation hearing for Supreme Court nominee Brett Kavanaugh in Hart Building on September 4, 2018.

One of the core choices Democrats will face in picking their 2020 nominee is whether to nominate a candidate best suited to mobilize younger and nonwhite voters who don't usually turn out, or one most effective at reassuring center-right whites who usually vote Republican but have recoiled from Trump on personal and cultural grounds. (The first group could include Sen. Kamala Harris of California, O'Rourke and Sen. Cory Booker of New Jersey; the second Joe Biden, Michael Bloomberg and an array of current and former governors.) That debate carries a clear geographic implication: "Mobilization" candidates are probably best positioned to compete in the Sun Belt, while "reassurance" candidates may be more effective in the Rust Belt.

The 2018 results leave both paths open to Democrats -- and indeed they indicate that Democrats must compete on both fronts, because they are not guaranteed success on either. When Trump himself is on the ballot -- and able to create contrasts, particularly around cultural and racial issues, with a Democratic nominee -- Democrats may struggle to hold the ground they regained earlier this month with working-class whites in the big Rust Belt battlegrounds.

Even so, the clearest signal from this month's results may be a variation on the old dictum from the legendary Ohio State football coach, Woody Hayes. Stressing a straightforward running game over a flashier passing attack, Hayes famously declared that the best route to victory on the football field was "three yards and a cloud of dust."

For all the glitter of their new Sun Belt opportunities, Democrats eyeing the cracks in Trump's armor that emerged this month in Wisconsin, Michigan and Pennsylvania may likewise conclude that the surest path to success in 2020 will be "three states and a cloud of dust."