For more than a century, Missouri was a bellwether state in the presidential election, backing the winning candidate in every contest but one between 1900 and 2004.

That changed in 2008, when Republican candidate John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE defeated Democrat Barack Obama Barack Hussein ObamaDemocratic Senate campaign arm outraises GOP by M in August A federal court may have declared immigration arrests unconstitutional Blunt says vote on Trump court nominee different than 2016 because White House, Senate in 'political agreement' MORE in Missouri by less then 4,000 votes, even as he was soundly defeated across the country.

For Democrats, it was an ominous sign of troubling trends to come, overshadowed by Obama's rout.

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The Show Me State is now solidly in the Republican column on the electoral college scoreboard. And Republicans hope to leverage their gains in 2018, when Sen. Claire McCaskill Claire Conner McCaskillMomentum growing among Republicans for Supreme Court vote before Election Day Democratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally MORE (D), one of the most vulnerable Democrats in the Senate, faces re-election.

More than that, the same demographic changes turning Missouri from purple to red are taking place throughout the Midwest, and could cost Democrats going forward.

“Missouri was the canary in the coal mine for Democrats,” said Tom Bonier, a Democratic data analytics expert. “Missouri 20 years ago was a swing state. All the sudden it just fell off the table, and it was white working class voters just flocking away from the party.”

This is the eighteenth story in The Hill’s Changing America series, in which we investigate the demographic and economic trends shaping the face of American politics today. No state represents the exodus of once-reliably Democratic voters better than Missouri.

For years, Missouri represented the nation in miniature. Its politics played out on the tug and pull between St. Louis, a culturally eastern city, and Kansas City, a culturally western city. The north is a rural breadbasket, and the south is a socially conservative Bible Belt.

“Missouri used to be a really good microcosm of America,” said John Hancock, a Republican strategist and former chairman of the state GOP. “It was a very good snapshot of the country.”

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Razor-thin presidential elections were decided in the suburban counties that ring St. Louis and Kansas City. Democrats ran up their vote totals in the cities, offset by big Republican margins in rural areas and in the southwest, around Springfield and Joplin.

At the same time, those rural voters long backed conservative Democrats like the late Ike Skelton, a hawk who frequently bucked his national party.

But as the nation has changed, Missouri has stayed much the same. The state has become older and whiter, according to U.S. Census Bureau data, and the influx of Hispanic Americans that changes the political calculus in other states has not materialized here; just 4 percent of Missourians are Hispanic, far below the national average.

“We don’t have an immigrant population here, a Hispanic population that looks anything like what it does across the country,” Hancock said.

White voters, especially those without a college degree, now play a more influential role in Missouri than they do in most other states. As partisan polarization has driven those voters to the Republican Party, Missouri Democrats have suffered.

“The story of Missouri as a swing state is a state being left behind by the politics of earlier times,” said Dave Robertson, who chairs the political science department at the University of Missouri-St. Louis. “The white population of Missouri has remained closer to the kind of 1950s demographic strength than has been true in other states.”

Nowhere is that shift more evident than in Missouri’s rural counties. In 1996, Bill Clinton William (Bill) Jefferson ClintonBattle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates Bill Clinton on GOP push to fill Ginsburg vacancy: Trump, McConnell 'first value is power' MORE won 62 of Missouri’s 114 counties, along with the independent city of St. Louis. Four years later, Al Gore Albert (Al) Arnold GoreCruz says Senate Republicans likely have votes to confirm Trump Supreme Court nominee 4 inconclusive Electoral College results that challenged our democracy Fox's Napolitano: 2000 election will look like 'child's play' compared to 2020 legal battles MORE won 13 counties and St. Louis. Obama won eight counties in 2008, and three in 2012, the same number Clinton won four years later.

Skelton was a victim too: He lost his seat in 2010, despite having voted against the Affordable Care Act.

In other states, Republican gains in rural areas have been offset by Democratic gains in cities, where minority voters and Millennials have boomed as shares of the population. But in Missouri, Republican gains in rural areas far outstrip Democratic advantages in big cities.

George W. Bush won only three Missouri counties with more than 70 percent of the vote in 2000; in 2016, 97 counties gave President Trump 70 percent or more. Between 2000 and 2016, all but two of Missouri’s counties trended towards Republicans.

Skelton’s successor, Rep. Vicky Hartzler (R), has won re-election three times with more than 60 percent of the vote. Across the state, Republicans now control both chambers of the state legislature and all but one statewide office.

Missouri shows signs of an emerging political divide, too, one between those with college educations and those who did not receive a college degree. Among the 50 Missouri counties that shifted 20 or more points toward Republicans between 2012 and 2016, just 14 percent of residents hold a college degree. In the three counties that became more Democratic, more than 31 percent of residents hold a degree.

Democratic struggles among the white working class in Missouri presaged the party’s problems elsewhere in the Midwest. Trump crushed Clinton in the nine Missouri counties that border Iowa, by a nearly four-to-one margin. Iowa voted for Trump by almost ten points. Ohio, Michigan and Wisconsin, states that look demographically similar to Missouri, also went for Trump.

“White working class voters in Ohio were performing like white working class voters in Missouri, who long since abandoned the party,” Bonier said.

At a time when Democrats searching for a path back to power say they must begin showing up in rural America, the vulnerable McCaskill stands out as a model. McCaskill’s office makes a concerted effort to put her in rural and conservative settings, even if she gets booed.

McCaskill made nearly 100 trips to Greene County, in Springfield, ahead of her re-election bid in 2012. She won Greene County by four percentage points that year, even as President Obama lost to Mitt Romney there by a nearly 25-point margin. McCaskill also won Buchanan County, north of Kansas City, outperforming Obama by nine points.

But five years ago, McCaskill beat out Todd Akin, the former Republican congressman whose campaign imploded amid ill-considered comments about abortion and rape. Next year, McCaskill is likely to face Attorney General Josh Hawley (R), a far more disciplined candidate. McCaskill’s survival will depend on winning over voters for which Hillary Clinton Hillary Diane Rodham ClintonBiden leads Trump by 36 points nationally among Latinos: poll Democratic super PAC to hit Trump in battleground states over coronavirus deaths Battle lines drawn on precedent in Supreme Court fight MORE and other down-ballot Democrats didn’t even compete.

“There are fewer socially conservative Democrats in the party,” Robertson said. “Democrats have abandoned rural areas to Republicans. They’re just not competing.”