Former Vice President and presidential nominee Joe Biden gives remarks at UA Plumbers Local 27 Erie Training Center in Erie, PA on October 10, 2020.Demetrius Freeman | The Washington Post | Getty ImagesDemocratic presidential nominees had not set foot in Erie, Pennsylvania, in a dozen years.When Joe Biden spoke at a union building there on Saturday, his very presence showed how one election turned the Rust Belt city from an afterthought into a priority for Democrats.President Barack Obama and his running mate Biden trounced their GOP opponents in Erie County in 2008 and 2012. Then in 2016, Republican President Donald Trump carried the area by about 2,000 votes as he leveraged concerns about manufacturing job losses and promised to revamp U.S. trade deals.Pennsylvania, where Biden was born, will award 20 electoral votes as one of the country’s top prizes. Erie County will help to test whether Biden’s economic message can break through in the Keystone State’s former Democratic strongholds — and others across the Midwest — that gave a Republican political newcomer a try four years ago.”I really look at Erie County as a bellwether county not just for Pennsylvania, but for counties like it across the United States, particularly the Rust Belt area throughout the Midwest,” said Joseph Morris, chair of the political science department at Mercyhurst University in Erie. “It is just so typical of counties in the Midwest that once had an industrial base that has seen that industrial base evaporate in three decades.”Erie County will offer one of the better tests in Pennsylvania of how effectively the rivals can tailor their messages to working-class people, according to political observers in the area. With an 87% White population and a lower percentage of college graduates than the country as a whole, the area is home to some of the White working class Trump had success reaching in 2016. Low turnout in the area among people of color — whom exit polls found overwhelmingly backed Clinton in Pennsylvania — also reflects the struggles Democrats had winning over non-White voters in the Midwest in 2016.In Erie on Saturday, Biden depicted an out-of-touch “Park Avenue” president who broke his promises to the working class and presided over an “unequal recovery” from the post-pandemic economic crisis. He questioned what the “bottom half” got while investors and corporate titans saw their net worth balloon.Trump held a rally Tuesday in the former steel and iron hub of Johnstown, which sits east of Pittsburgh, and delivered a message familiar to Erie County’s voters. He said free-trade policies backed by Biden “decimated entire towns in your area,” arguing “China wins” if the Democrat prevails on Nov. 3.Biden chose to focus on the economy in an area that has recovered more slowly from the coronavirus-related shutdowns than the country as a whole. Erie County had an 11.1% unemployment rate in August — higher than the Pennsylvania and national marks of 10.3% and 8.4%, respectively.The Democrat touted his recovery plan, which aims to boost the economy by promoting American-made products, revamping U.S. infrastructure, investing in clean energy, enacting a $15-per-hour minimum wage and putting in place stronger workplace safety requirements.Meanwhile, in a Pennsylvania speech interspersed with horror stories about what the country would become under Biden’s watch, Trump highlighted his efforts to reduce regulations, update the North American Free Trade Agreement and cut taxes for many Americans as part of the 2017 GOP law. He highlighted the health of the U.S. economy before the virus hit — a point local Republicans aim to stress as they try to hold the ground gained in 2016.”People look for results, and they got results that were great at least until the Covid impact took place,” said Verel Salmon, chairman of the Erie County Republican Party.The county had a much lower unemployment rate of 5.8% in February, though it still stood higher than the statewide rate of 4.7%. A Mercyhurst poll of Erie County voters taken in February found 58% of respondents approved of how Trump was handling the economy at the time.But a majority or plurality of voters disapproved of how Trump was handling 10 of the 14 issues included in the survey.”They may be really satisfied with what he’s doing with the economy, but with everything else, they have a great deal of concern,” Morris said.Why Erie is in playBefore 2016, Democrats had not lost Erie County in a presidential election in this century. Obama won it by about 20 percentage points in 2008. His margin narrowed in 2012, but to a still-commanding 16 percentage points.Then, Trump won Erie County by about 1.5 percentage points in a dramatic shift. His edge of nearly 2,000 votes, which followed Obama’s roughly 19,000-vote victory, came during a 2016 election in which he won Pennsylvania by an overall margin of only about 44,000 votes.Erie County Democratic Party Chair Jim Wertz, who did not lead the party in 2016, said the city of Erie saw low turnout in precincts with high shares of people of color and immigrants during that election. He added that the party saw a “momentary lapse” in Democratic commitment to nominee Hillary Clinton, especially in a county where about 47% of primary voters supported Sen. Bernie Sanders over her in 2016.When many county voters saw an “outsider” in Trump, “they gave him a shot,” Wertz said.Wariness of Clinton contributed to Trump’s success in Erie County, said Anjali Sahay, program director of political science at Gannon University in Erie. “Industrial decline” and Trump’s pledges to jolt the manufacturing sector again compounded problems for Democrats, she added.”I think people were just ready for a change,” Sahay said.The manufacturing drain has continued, despite overall economic improvements in Erie before the coronavirus hit. General Electric, once a driver of Erie’s economy, moved hundreds of jobs to Texas in recent years. Wabtec ultimately merged with GE Transportation, and still runs a manufacturing facility in Erie.The shift toward the GOP did not hold in the 2018 midterms. Both Democratic U.S. Sen. Bob Casey and Gov. Tom Wolf won the county by at least 18 percentage points during a strong year for the party in Pennsylvania.During the Trump presidency, “the No. 1 issue that really resonates with everybody is the effect this administration has had on democratic institutions and the democratic process,” said Wertz, the county Democratic Party chair. He added that the party has focused on health care, jobs, education and infrastructure in the runup to the Nov. 3 election.But Republicans have seen recent trends that make them hopeful about a Trump repeat in Erie County. Democrats held a voter registration advantage of 98,319 to 73,238 in the county as of earlier this week, according to state records, but Republicans have narrowed the gap.The number of registered Republicans in the county has jumped by more than 5,700 since November 2016, while the number of Democrats on the rolls has increased by only 722. It reflects a broader climb in Republican registrations across Pennsylvania.”We see it as a positive indicator of the way the county is moving,” said Salmon of the county GOP.Where Erie County will be decidedMorris said people in Erie County generally divide the area politically by Interstate 90, which runs roughly parallel to the shore of Lake Erie as it cuts from Ohio to New York. The Democratic-leaning city of Erie and some of its most populated suburbs sit north of the highway, while rural areas and smaller cities and boroughs with a higher concentration of Republican voters lie to the south.For Trump to repeat his 2016 success, he likely has to take as many votes from Biden as he can in the northern part of the county, while running up the margins below I-90, Morris said.The local parties’ strategies reflect how their calculus in Erie County has changed. Wertz said the county Democratic Party set up field offices outside of the city of Erie for the first time ever this year.It established an arm in Millcreek Township, the city’s most populous suburb, which local observers consider a swing area within the battleground county. Democrats have also focused on North East, a borough near the state’s border with New York, and Union City, a borough in the southern part of the county.Trump outperformed Republican Mitt Romney’s 2012 campaign in all of those areas.Biden’s messaging in his Erie stop offered a view of the message he will use to try to win back the states of Pennsylvania, Michigan and Wisconsin. He argued Trump’s difficulty in containing the virus outbreak led to unnecessarily sustained and deep economic pain for Americans.He raised the threat of Republicans repealing the Affordable Care Act. Pennsylvania, which expanded Medicaid under the ACA, had one of the lower uninsured rates in the nation at about 6% in 2018.Erie does not rely on the natural gas industry and the divisive practice of fracking in the way southwestern Pennsylvania does. Even so, he stressed in Erie that he is “not banning fracking, period.”Trump and his allies have tried to use prominent Democrats’ opposition to fracking to win support in the areas surrounding Pittsburgh, which helped to make Pennsylvania the second-largest natural gas-producing state last year. Many Democrats have pushed to stop the practice due to concerns about water and air pollution from chemicals used in the process.The focus on those issues shows Biden’s and Trump’s effort to appeal to the working-class people who drove Trump’s success in Erie County.”The working man, the working woman, the working families and so forth are certainly the major thing. Those are the people that said, ‘We want results,’ and have continued to say that,” Salmon said.But in an election year shaped in every way by the devastation wrought by the pandemic, the winner may well be the candidate who offers the most compelling case that they can create some semblance of normal life.For Biden, it means containing the virus and shaping what he calls a fairer and cleaner economy. For Trump, it means returning to what the country and economy looked like in February.”That is what people want, a return to normalcy, whether it’s an end to the pandemic, an end to unemployment. … Whoever can do that I think is going to be the winner,” Gannon’s Sahay said.Subscribe to CNBC on YouTube.