U.S. Rep. Dwight Evans calls his field director to the phone. There's a telling statistic he wants.

In the neighborhoods that make up his congressional district, which includes North Philadelphia, voter turnout in the 2014 midterm election was 40 percent. Two years later, in a presidential election, it bloomed to 73.5.

The contrast helps explain why former President Barack Obama is coming to North Philadelphia on Friday to rally local voters on behalf of U.S. Sen. Bob Casey, Gov. Wolf, and other Democrats down the ballot.

He'll be speaking at the Dell Music Center, famous for decades of jazz and R&B concerts, a place Evans called "a great venue" to reach the city's black community.

"It's a very positive venue relating specifically for African Americans," said Evans, a Democrat whose district is nearly 60 percent black, according to Census Bureau estimates. "It brings you a presence in the heart of the neighborhood."

Democrats have seen a surge of energy in suburban areas, including those immediately outside of Philadelphia, and expect it to continue as voters are motivated by critical House races on the ballot in November. There isn't the same fall drama in a city like Philadelphia, where Democrats already hold every major office — but the party still needs its trove of voters to help reelect Wolf and Casey, and as it maps a path aimed at winning back the state in 2020.

Democrats saw a slight dip in Philadelphia in 2016 in the wake of Obama's outsize appeal. Hillary Clinton's vote total in the city fell 17,000 votes short of Obama's in 2012, even as she outperformed him in suburbs like Chester and Delaware Counties.

Meanwhile, President Trump was scoring blockbuster totals beyond the southeast corner — he won Pennsylvania by 44,000 votes, the first Republican to claim the state's 20 electoral votes since 1988.

Democrats running this year see a two-prong approach: appealing to crossover voters who supported Trump, and reigniting stalwart Democrats.

"If there's a huge amount of enthusiasm in Philadelphia and in Pittsburgh, it often can be the difference-maker" regardless of what happens elsewhere in the state, said Gabe Morgan, the Pennsylvania and Delaware state director for the Service Employees International Union.

With Democrats seeking wins both in moderate suburbs and in cities that are trending farther left, Obama is a figure the party can rally around, he said.

"Obama is still, in cities, a unifying figure," Morgan said.

Republicans, however, argue that Obama can also energize the right.

U.S. Rep. Lou Barletta, the Republican challenging Casey and hoping to re-create the rural and working-class coalition that supported Trump, pointed to Obama's 2008 comments that people in small towns in Pennsylvania and the Midwest "cling to guns or religion" after being frustrated by broken promises to revive their economic fortunes.

In a release referring to Obama's coming rally as a lecture, Barletta spokesman David Jackson asked: "Does Casey believe that the people of Lancaster, York, Altoona, and Butler 'cling to their guns and religion'? What does Bob Casey really think about the people of Pennsylvania?"

As Obama leaves the stage in Philadelphia on Friday, Donald Trump Jr. will be stepping to the microphone at the Pennsylvania Republican Party's annual fall dinner in Hershey.

"Right now, there's more intensity on the Democratic side, but clearly it's not as much as they'd like," said Val DiGiorgio, chairman of the state GOP. "That's why they're bringing Obama in, to increase that."

DiGiorgio said Trump Jr. is helping drive an uptick in Republican excitement. As of Wednesday, the party had sold more than 600 tickets to Friday's dinner, a response rate DiGiorgio said he had not seen before, he said. Sponsorship at the dinner tops out at $10,000 while a general admission ticket goes for $150.

After the rally at the Dell, Obama will head to a more exclusive Center City location to host a fund-raiser for Casey and Democrats' Senate campaign arm. Tickets range from $1,000 to $33,900.

He and Casey were Senate colleagues and played basketball together, and Casey supported Obama in the 2008 Pennsylvania primary.

Democrats hope Obama's obvious appeal to African Americans can encourage a key demographic for the party to vote Nov. 6. A Politico/Morning Consult national poll released Wednesday found that 66 percent of white voters are "very enthusiastic" about voting this fall, compared to 58 percent of African Americans and 52 percent of Hispanics.

Philadelphia Democrats noted that media coverage of the Obama rally will reach into competitive suburban areas where the party is pushing for gains in U.S. House races, and several downplayed the idea of a rally targeting any one group.

"He stimulates people. I don't want to say he's just coming to Philly to energize the black voters. I think he's coming to energize everyone," said former City Councilwoman Marian Tasco, a leader in the African American political community known as the Northwest Coalition.

U.S. Rep. Bob Brady, chairman of the city's Democratic Party, said, "Barack Obama is going to attract African Americans automatically. … They're in love with him." But he said he didn't think the event was orchestrated for that reason.

U.S. Rep. Brendan Boyle, a Philadelphia Democrat, downplayed concerns about his party's 2016 results in Philadelphia. Clinton still got more votes in the city than Democratic nominees John Kerry in 2004 and Al Gore in 2000, he said.

Counting the suburbs and city together, she actually performed better in Southeast Pennsylvania overall than Obama did in 2012 — which helped magnify Democrats' shock when Trump carried the state anyway.

It's also a reason why Democrats are turning to Obama to juice what they believe is already a substantial enthusiasm advantage.

After 2016, Boyle said, "you don't want to leave anything on the table."

Staff writer Jonathan Lai contributed to this article.