Gregory Korte

USA TODAY

PHILADELPHIA — President Obama went after Donald Trump on the campaign trail on Tuesday, attacking the Republican presidential nominee for his business ethics, his affinity for Russian President Vladimir Putin and his pessimistic vision of America.

"I keep on reading this analysis that Trump's got support from working folks. Really? This is the guy you want to be championing working people?" Obama said at a campaign rally in Philadelphia. "The guy who spent 70 years on this earth showing no concern for working people?

"He wasn't going to let you on his golf course, He wasn’t going to let you buy into his condo. And now he wants to be your champion?"

With Democratic presidential candidate Hillary Clinton sidelined by pneumonia, Obama rolled up his shirtsleeves and stepped into the 2016 campaign with a stop in Philadelphia designed to bring out the voters that helped him to carry Pennsylvania twice.

Obama's campaign trip to Philadelphia — his first appearance on the trail since a joint appearance with Clinton in Charlotte in July — was scheduled weeks ago. But the timing was serendipitous, giving the surrogate-in-chief top billing in a key electoral battleground while Clinton recuperates at home.

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But Obama's appeal seemed directed as much at Republicans as the Democratic loyalists who packed a downtown Philadelphia park.

Several times, Obama contrasted Trump's brand of conservatism with that of President Ronald Reagan. "He called America a shining city on a hill. Donald Trump calls it a divided crime scene."

Noting that Trump appeared on Russian state television last week, Obama accused Trump of trying to "curry favor" with Putin.

"He loves this guy. Think about what’s happened to the Republican party, Obama said. "Can you imagine Ronald Reagan idolizing someone like that?"

And in a Trump-like turn, Obama even addressed a complaint to the reporters at the back. "I'm not running this time, but I sure do get frustrated by the way this campaign is being covered. Guys in the back, I'm just telling the truth about how I feel about this," he said.

"You don’t grade the presidency on a curve. This is serious business. And when we see folks talking about transparency — you want to debate transparency? You have one candidate in this race who's released decades worth of her tax returns. You have another candidate who is the first in decades who refuses to release any and all."

The Clinton campaign said 6,000 people packed the rally in Philadelphia's Eakins Oval, a park at the bottom of the steps to the Philadelphia Art Museum's made famous by the movie Rocky. The steps themselves were fenced off, framed by giant letters spelling out the Clinton campaign slogan: "Stronger Together."

"Can I just say, I am really into electing Hillary Clinton. This is not me going through the motions here. I really, really, really want to elect Hillary Clinton," Obama said. "Sometimes folks are kind of surprised by that because they remember, man, you guys had a tough fight eight years ago. Every time I thought I was ahead, it was like climbing up the Rocky steps."

Both campaigns are fighting over Philadelphia — and especially its middle-class suburbs — as educated white voters have turned into a swing demographic. Donald Trump was scheduled to come to those same suburbs Tuesday night for a speech on childcare aimed at winning over women.

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With Clinton off the trail for two days, Obama was part of a high-powered surrogate lineup that also included her daughter Chelsea Clinton, running mate Tim Kaine, his wife Anne Holton, former president Bill Clinton and first lady Michelle Obama.

Afterward, Obama was scheduled to headline a number of fundraisers in Philadelphia and New York to benefit the Democratic National Committee, which will pay the cost of the president's campaign trip on Air Force One.

White House Deputy Press Secretary Eric Schultz told reporters to expect more presidential campaign trips in the coming weeks.