The battle for control of both the White House and the U.S. Senate will center on an overlapping handful of Sun Belt states that will test whether demographic changes and President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE’s dismal approval ratings can alter the political map.

To win back control of the Senate, Democrats acknowledge they will have to rely in part on their presidential nominee competing in states that have not voted for a Democratic presidential candidate for a generation or more.

At the same time, Republicans running for reelection find it difficult or untenable to separate themselves from President Trump, despite his dismal approval ratings, because he still enjoys the ardor of so many Republican base voters.

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That is in part because the polarization of American politics has made it more difficult for a Democrat or a Republican to craft their own identities separate from their national parties.

In 2016, for the first time since direct elections of senators began a century ago, no state elected a senator from the party that did not win that state’s electoral votes.

“We’ve seen this kind of trend of nationalization of politics up and down the ballot,” said Jonathan Kappler, executive director of the center-right North Carolina Free Enterprise Foundation.

Next year, there are only four senators seeking reelection in states the other party’s presidential candidate won in 2016: Sens. Doug Jones (D-Ala.), Gary Peters Gary Charles PetersBiden's six best bets in 2016 Trump states GOP set to release controversial Biden report Democrats fear Russia interference could spoil bid to retake Senate MORE (D-Mich.), Cory Gardner Cory Scott GardnerOvernight Health Care: US coronavirus deaths hit 200,000 | Ginsburg's death puts future of ObamaCare at risk | Federal panel delays vote on initial COVID-19 vaccine distribution The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-Colo.) and Susan Collins Susan Margaret CollinsSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-Maine).

Republicans hold 53 of the 100 seats in the U.S. Senate, meaning Democrats have to pick up a net of three seats and the White House, or four seats without the presidency, to reclaim control.

Most Democrats believe Jones, elected in a special election against a scandal-plagued candidate, is all but certain to lose his seat, adding another hurdle to their chances.

Where the 2016 Senate map focused on Rust Belt states like Pennsylvania, Wisconsin and New Hampshire, the 2020 battlegrounds will largely be focused in Sun Belt states — states that have traditionally voted Republican in presidential contests, but where changing demographics give Democrats renewed hope.

To win the seats they need to reclaim the majority, Democrats will look first to Arizona, where Sen. Martha McSally Martha Elizabeth McSallyTumultuous court battle upends fight for Senate Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee The Hill's Campaign Report: Biden goes on offense MORE (R) will seek a full term after being appointed to the seat last year.

McSally lost a narrow race against now-Sen. Kyrsten Sinema (D) in 2018, though no Democrat has carried the state’s electoral votes since Bill Clinton William (Bill) Jefferson ClintonChelsea Clinton: Trump isn't building public confidence in a vaccine Hillary Clinton launching podcast this month GOP brushes back charges of hypocrisy in Supreme Court fight MORE in 1996.

Sen. Thom Tillis Thomas (Thom) Roland TillisThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting OVERNIGHT ENERGY: EPA head questions connection of climate change to natural disasters | Pebble Mine executives eye future expansion in recorded conversations | EPA questions science linking widely used pesticide to brain damage in children Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight MORE (R-N.C.) is likely to be a prime Democratic target too, in a state where Republicans have won six of the last eight U.S. Senate elections.

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And in Georgia, a state that hasn’t sent a Democrat to the Senate since Zell Miller won a special election in 2000, Democrats have pinned their hopes on former gubernatorial candidate Stacey Abrams (D).

And Democrats emboldened by former Rep. Beto O’Rourke’s (D-Texas) narrow loss to Sen. Ted Cruz Rafael (Ted) Edward CruzTrump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy MORE (R) hold out hopes for a better performance in a presidential year, when Sen. John Cornyn John CornynThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight Senate GOP faces pivotal moment on pick for Supreme Court MORE (R-Texas) seeks reelection.

Texas has not sent a Democrat to the Senate since Lloyd Bentsen (D) won reelection in 1988, but the state’s rapid growth has attracted new, more liberal residents who handed Democrats several House seats in 2018.

O’Rourke and Abrams, both liberals who came close to winning in conservative states, highlight the new approach some Democrats are taking.

Rather than plotting a course for centrist voters, those candidates charted a path that emphasized expanding turnout among core base voters.

“Most Democrats are running to the left, so there isn’t as much of a need to distance themselves from the national ticket. The era of moderation for the sake of being moderate is over. All politics start with building a strong base and then winning over the middle voters with the strength of your argument,” said Ed Espinoza, a Democratic strategist and executive director of Progress Texas, a progressive policy group.

If the party pursues the same strategy in 2020, the Democratic presidential nominee’s performance will be of added concern.

“Historically, the Democrats by and large tried to separate themselves from the national party,” Kappler said of his home state. “That changed in 2008; that was a clear threshold in North Carolina where the Obama campaign came in and nationalized things.”

Neither side is willing to overlook states where their presidential contender has little hope of competing, though many privately acknowledge the perils of depending on split-ticket voters.

Democrats have hopes of competing in Kansas, a state that last sent a Democrat to the Senate in 1932 but which elected a Democratic governor in 2018.

They are also likely to field a prominent candidate in Kentucky, where Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Senate GOP aims to confirm Trump court pick by Oct. 29: report Trump argues full Supreme Court needed to settle potential election disputes MORE (R) — a favorite villain of the left — will seek reelection. Kentucky last elected a Democratic senator in 1992.

Republicans are likely to woo New Hampshire Gov. Chris Sununu (R) to challenge Sen. Jeanne Shaheen Cynthia (Jeanne) Jeanne ShaheenSenate Democrats introduce bill to sanction Russians over Taliban bounties Trump-backed candidate wins NH GOP Senate primary to take on Shaheen Democratic senator urges Trump to respond to Russian aggression MORE (D) in a state Trump only narrowly lost in 2016.

Peters may draw a challenger, after Trump’s win in Michigan in 2016. And Sen. Tina Smith Tina Flint SmithThe Hill's Campaign Report: Trump and Biden vie for Minnesota | Early voting begins in four states | Blue state GOP governors back Susan Collins GOP Senate candidate says Trump, Republicans will surprise in Minnesota Biden promises Democratic senators help in battleground states MORE (D), who won a special election to serve a two-year term by 11 points in 2018, will seek reelection in Minnesota, a state Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE carried by just under 45,000 votes.

“The map’s not that small,” said J.B. Poersch, who runs the Senate Majority PAC, a Democratic super PAC.

But in an era of polarization, with a hyperpolarizing figure like Trump on the ballot, there are fewer voters willing to divide their tickets between presidential candidates and Senate candidates.

“The middle is gone,” Espinoza said. “Even the middle doesn’t want to be in the middle, they want to pick a team.”