(Reuters) - The road to the White House next year runs through a handful of U.S. states where the election is expected to be especially close due to changing demographics and the polarizing politics of Republican President Donald Trump.

Slideshow ( 3 images )

To better understand the dynamics driving the vote, Reuters identified four of the nation’s most competitive counties in these political battlegrounds and will report from them through the November 2020 election.

Several of the counties, like their states, swung from Democratic to Republican in the 2016 presidential contest. They reflect a variety of geographies and, according to a Reuters data analysis, populations diverse in age, education, employment and race.

They also are home to industries and issues that represent a broad cross-section of the American experience.

Though hardly the only counties that will be decisive in 2020, these four offer a window into the mood and motivations of the voters shaping the country’s political future.

* Racine County, Wisconsin: This county in the southeastern part of the state picked the winner of the last five U.S. presidential elections, going for Trump by 4 percentage points in 2016. A controversial multi-billion-dollar Foxconn manufacturing plant now under construction here is lauded by Trump as a chance to rebuild American manufacturing.

* Maricopa County, Arizona: Hispanic voters are a growing electoral force in the largest, most politically influential county of a state on the U.S.-Mexico border. In 2016, Trump’s 3-percentage point edge in Maricopa was the closest for a Republican president in years. In 2018, U.S. Senator Kyrsten Sinema, a Democrat, secured her win by flipping the county.

* Northampton County, Pennsylvania: This predominantly white county is becoming more racially diverse even as it flipped to the Republicans in 2016. Trump captured Northampton County by 4 percentage points after Democrats won it in the four prior presidential elections.

* Pinellas County, Florida: This sprawling county on Florida’s central west coast voted for Trump by about 1 percentage point, a razor-thin margin in a state where elections are always tight. Though Democrats won the county comfortably in the 2008 and 2012 White House races, it now includes almost the same number of registered Democrats and Republicans.

Reuters selected the counties in this series after examining, among other factors, voting patterns, demographics, population trends and economic statistics for more than 700 U.S. counties across a total of seven states that political strategists expect to be closely fought.

Reuters gathered its data from state elections offices; the U.S. Census Bureau; the Center for American Progress, a liberal think tank; and the County Health Rankings & Roadmaps program at the University of Wisconsin Population Health Institute.

(For an interactive version of this story: tmsnrt.rs/2IrnBXR)